I really hate that people call Linux distributions 'X OS' and you get sites like this which at no point clarify where it is actually a distro or an entirely new OS.
It is confusing and somewhat disrespectful towards Linux.
Linux is just an implementation detail; it's a more accurate description to call it a GNU/Linux system, yes, but most Linux distros could drop in one of the BSDs or illumos as their base layer and from a user perspective nothing would change.