Kernel is the major thing under GPL left and while there are some theories they might want to replace it with the Fucsia micro kernel I don't think they have a chance in hell given the ministered and number of parties involved in cooperative Linux kernel development.
It’s not a desktop Linux OS, of course. But it’s still Linux.
Often, for specific devices, the kernels they run are forks with changes that aren't upstreamed. Some of those changes can be significant enough that porting those changes to an updated kernel snapshot is nearly impossible, so it never happens, despite the kernel fork's source being available under the GPLv2.
[1] https://android.googlesource.com/platform/ndk/+/4e159d95ebf2...
That is what makes a linux distribution too me in my opinion, in the same way I can run a linux with musl libc, and busybox, I can run Android
The overall Android environment isn't Debian, Ubuntu, RedHat, ..., or other GNU/Linux environment.
(the downvotes you currently have there given the graying text are a bit misguided IMO, your misconception is a very common one, one that people in some circles even seen to encourage)