Again, GNU is an operating system. GNU utilities are utilities. You can port them wherever you want. Doesn't mean that all the software will suddenly get ported with it.

GNU is colloquially all the software that runs on top of Linux and glibc. Because it's an entire string of dependencies. You may argue that all this also works on musl. I'd argpe that it doesn't, the work is still going on, and even if it did, the whole system (musl+Linux) would be more like a GNU clone. The same way GNU is a Unix clone. Stallman wrote the GNU software to replace Unix. Before Linux came along, all this software worked with Unix. So it's complicated.

I'm not going to claim that Linux with musl is necessarily GNU+Linux but it's at least GNU-compatible. Again. Windows worked with DOS software. It still does, the cmd is a remnant of DOS. The main question is the border between an original and a clone.