`SIGTTOU` signal to the background process - bash

Question

As per the post, which says that[emphasis mine]:
If a process within a background job tries to write to a TTY device, the TTY sends a SIGTTOU signal to the entire job. This will normally suspend the job. It is possible to turn off this feature on a per-TTY basis.
If I understand that statement correctly, there should be no output when invoking ls / & since the ls would receive the SIGTTOU signal when trying to write out, which would suspend the running of ls.
But there is output in the terminal when calling ls /&, which is really out of my expectation.
Here is the output:
ls / &
[1] 75297
jhon#desktop:~$ initrd.img lib32 lost+found opencv_4.0.tar.gz sbin tmp vmlinuz
bin data-ceph data2 etc lfs lib64 media opt root srv usr zeus
boot data.bk dev home lib libx32 mnt proc run sys var
#the cursor twinkles until I hit the enter key.
#empty line
[1]+ Done ls /
jhon#desktop:~$
Am I misunderstanding the aforementioned statement? If I am wrong, please let me know.
What's more, it seems that no SIGTOU signal is ever sent to ls. Here is the output of strace ls / &
strace ls / &
[1] 80908
jhon#desktop::~$ execve("/bin/ls", ["ls", "/"], [/* 29 vars */]) = 0
brk(0) = 0x9d8000
access("/etc/ld.so.nohwcap", F_OK) = -1 ENOENT (No such file or directory)
access("/etc/ld.so.preload", R_OK) = -1 ENOENT (No such file or directory)
open("/etc/ld.so.cache", O_RDONLY|O_CLOEXEC) = 3
fstat(3, {st_mode=S_IFREG|0644, st_size=122346, ...}) = 0
mmap(NULL, 122346, PROT_READ, MAP_PRIVATE, 3, 0) = 0x7f00e80f2000
close(3) = 0
access("/etc/ld.so.nohwcap", F_OK) = -1 ENOENT (No such file or directory)
open("/lib/x86_64-linux-gnu/libselinux.so.1", O_RDONLY|O_CLOEXEC) = 3
read(3, "\177ELF\2\1\1\0\0\0\0\0\0\0\0\0\3\0>\0\1\0\0\0\0[\0\0\0\0\0\0"..., 832) = 832
fstat(3, {st_mode=S_IFREG|0644, st_size=134296, ...}) = 0
mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f00e80f1000
mmap(NULL, 2238192, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0x7f00e7ccb000
mprotect(0x7f00e7ceb000, 2093056, PROT_NONE) = 0
mmap(0x7f00e7eea000, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x1f000) = 0x7f00e7eea000
mmap(0x7f00e7eec000, 5872, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) = 0x7f00e7eec000
close(3) = 0
access("/etc/ld.so.nohwcap", F_OK) = -1 ENOENT (No such file or directory)
open("/lib/x86_64-linux-gnu/libacl.so.1", O_RDONLY|O_CLOEXEC) = 3
read(3, "\177ELF\2\1\1\0\0\0\0\0\0\0\0\0\3\0>\0\1\0\0\0`\34\0\0\0\0\0\0"..., 832) = 832
fstat(3, {st_mode=S_IFREG|0644, st_size=31168, ...}) = 0
mmap(NULL, 2126336, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0x7f00e7ac3000
mprotect(0x7f00e7aca000, 2093056, PROT_NONE) = 0
mmap(0x7f00e7cc9000, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x6000) = 0x7f00e7cc9000
close(3) = 0
access("/etc/ld.so.nohwcap", F_OK) = -1 ENOENT (No such file or directory)
open("/lib/x86_64-linux-gnu/libc.so.6", O_RDONLY|O_CLOEXEC) = 3
read(3, "\177ELF\2\1\1\0\0\0\0\0\0\0\0\0\3\0>\0\1\0\0\0P \2\0\0\0\0\0"..., 832) = 832
fstat(3, {st_mode=S_IFREG|0755, st_size=1857312, ...}) = 0
mmap(NULL, 3965632, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0x7f00e76fa000
mprotect(0x7f00e78b8000, 2097152, PROT_NONE) = 0
mmap(0x7f00e7ab8000, 24576, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x1be000) = 0x7f00e7ab8000
mmap(0x7f00e7abe000, 17088, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) = 0x7f00e7abe000
close(3) = 0
access("/etc/ld.so.nohwcap", F_OK) = -1 ENOENT (No such file or directory)
open("/lib/x86_64-linux-gnu/libpcre.so.3", O_RDONLY|O_CLOEXEC) = 3
read(3, "\177ELF\2\1\1\0\0\0\0\0\0\0\0\0\3\0>\0\1\0\0\0\260\27\0\0\0\0\0\0"..., 832) = 832
fstat(3, {st_mode=S_IFREG|0644, st_size=252032, ...}) = 0
mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f00e80f0000
mmap(NULL, 2347200, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0x7f00e74bc000
mprotect(0x7f00e74f9000, 2093056, PROT_NONE) = 0
mmap(0x7f00e76f8000, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x3c000) = 0x7f00e76f8000
close(3) = 0
access("/etc/ld.so.nohwcap", F_OK) = -1 ENOENT (No such file or directory)
open("/lib/x86_64-linux-gnu/libdl.so.2", O_RDONLY|O_CLOEXEC) = 3
read(3, "\177ELF\2\1\1\0\0\0\0\0\0\0\0\0\3\0>\0\1\0\0\0\320\16\0\0\0\0\0\0"..., 832) = 832
fstat(3, {st_mode=S_IFREG|0644, st_size=14664, ...}) = 0
mmap(NULL, 2109744, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0x7f00e72b8000
mprotect(0x7f00e72bb000, 2093056, PROT_NONE) = 0
mmap(0x7f00e74ba000, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x2000) = 0x7f00e74ba000
close(3) = 0
access("/etc/ld.so.nohwcap", F_OK) = -1 ENOENT (No such file or directory)
open("/lib/x86_64-linux-gnu/libattr.so.1", O_RDONLY|O_CLOEXEC) = 3
read(3, "\177ELF\2\1\1\0\0\0\0\0\0\0\0\0\3\0>\0\1\0\0\0\300\20\0\0\0\0\0\0"..., 832) = 832
fstat(3, {st_mode=S_IFREG|0644, st_size=18624, ...}) = 0
mmap(NULL, 2113760, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0x7f00e70b3000
mprotect(0x7f00e70b7000, 2093056, PROT_NONE) = 0
mmap(0x7f00e72b6000, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x3000) = 0x7f00e72b6000
close(3) = 0
mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f00e80ef000
mmap(NULL, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f00e80ed000
arch_prctl(ARCH_SET_FS, 0x7f00e80ed840) = 0
mprotect(0x7f00e7ab8000, 16384, PROT_READ) = 0
mprotect(0x7f00e72b6000, 4096, PROT_READ) = 0
mprotect(0x7f00e74ba000, 4096, PROT_READ) = 0
mprotect(0x7f00e76f8000, 4096, PROT_READ) = 0
mprotect(0x7f00e7cc9000, 4096, PROT_READ) = 0
mprotect(0x7f00e7eea000, 4096, PROT_READ) = 0
mprotect(0x619000, 4096, PROT_READ) = 0
mprotect(0x7f00e8110000, 4096, PROT_READ) = 0
munmap(0x7f00e80f2000, 122346) = 0
statfs("/sys/fs/selinux", 0x7ffcbb368ce0) = -1 ENOENT (No such file or directory)
statfs("/selinux", 0x7ffcbb368ce0) = -1 ENOENT (No such file or directory)
brk(0) = 0x9d8000
brk(0x9f9000) = 0x9f9000
open("/proc/filesystems", O_RDONLY) = 3
fstat(3, {st_mode=S_IFREG|0444, st_size=0, ...}) = 0
mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f00e810f000
read(3, "nodev\tsysfs\nnodev\trootfs\nnodev\tr"..., 1024) = 400
read(3, "", 1024) = 0
close(3) = 0
munmap(0x7f00e810f000, 4096) = 0
ioctl(1, SNDCTL_TMR_TIMEBASE or SNDRV_TIMER_IOCTL_NEXT_DEVICE or TCGETS, {B38400 opost isig -icanon -echo ...}) = 0
ioctl(1, TIOCGWINSZ, {ws_row=35, ws_col=169, ws_xpixel=169, ws_ypixel=35}) = 0
stat("/", {st_mode=S_IFDIR|0755, st_size=4096, ...}) = 0
openat(AT_FDCWD, "/", O_RDONLY|O_NONBLOCK|O_DIRECTORY|O_CLOEXEC) = 3
getdents(3, /* 38 entries */, 32768) = 1080
getdents(3, /* 0 entries */, 32768) = 0
close(3) = 0
fstat(1, {st_mode=S_IFCHR|0620, st_rdev=makedev(136, 89), ...}) = 0
mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f00e810f000
write(1, "VCAST_GUI_SIZES.plist data\t da"..., 140VCAST_GUI_SIZES.plist data data1 dms_windows_server initrd.img lib32 lost+found opencv_4.0.tar.gz reportlog.log sbin tmp vmlinuz
) = 140
write(1, "bin\t\t data-ceph data2 et"..., 96bin data-ceph data2 etc lfs lib64 media opt root srv usr zeus
) = 96
write(1, "boot\t\t data.bk\t dev\t home"..., 88boot data.bk dev home lib libx32 mnt proc run sys var
) = 88
close(1) = 0
munmap(0x7f00e810f000, 4096) = 0
close(2) = 0
exit_group(0) = ?
+++ exited with 0 +++
[1]+ Done strace ls /