Ah ok, I see what you mean. I've always thought of "operating system" as the kernel itself (and some set of user land tools as a "distribution") but I can see how it could be interpreted differently.

I mean, what counts as the "operating system" is not the point here. It's that, whatever "UNIX" is (operating system, distribution, or whatever you want to call it), is more than just the kernel, and can't meaningfully be said to be replicated by Linux without mentioning GNU.

I have found the easiest way for people to understand it is: Android runs a Linux kernel. The systems we often call "Linux" systems are really Linux + GNU + X to get to the same kind of place.

That is an interpretation at odds with UNIX history, and basically only applicable to Linux, which is the exception to the rule. I suggest reading this article, it's written for FreeBSD but applies very similarly to Solaris etc.

https://www.over-yonder.net/~fullermd/rants/bsd4linux/03