If you want to be this pedantic then GNU/Linux also isn't an OS. Debian is an OS, Arch is an OS. NixOS is an OS. Such statement muddy the water to the point of no longer matching at all what people mean. Because when people talk they don't use the 100% correct technical term.
So what's your point? When people say linux. You take it to mean GNU/Linux. And that honestly comes out of nowhere. At my work we use a ton of embedded devices that don't use GNU but instead use things like busybox. Everyone refers to them as Linux systems.
Android is Linux system in every single way. It's not however a GNU/Linux system. But the comment you originally replied didn't claim that.
