Linux is not exclusively GNU/Linux. For example, Musl/Linux (eg. Alpine Linux) and Android/Linux are widespread. The Linux ABI is unchanged.
Legitimate Linux applications are written in Go all the time. Linux applications are often written in Rust and use the Linux ABI without going through any libc. They seem to be doing mighty fine in terms of "being Linux".
This sounds like some variant of the True Scotsman fallacy.
Wow, this is a third commenter who didn't bother to read what OP wrote.
Come on! OP meant the whole OS, not the kernel project. How is this not obvious?