I don't think Posix is very relevant to what is or isn't linux.

macOS is more posix than NixOS, but everyone knows NixOS is a real linux distro, and macOS is not one.

Me neither! I was suggesting to use "Posix" instead of "Linux" because it properly separates GNU/Linux or other Linuxes from Android. Posix is what Android isn't but what MacOS is. What people erroneously try to call "Linux" because they don't have a better word.