Don't forget Alpine Linux, which almost everyone will call Linux because it has "Linux" in the name, but also doesn't use GNU, instead running the Linux kernel with musl and busybox as the C library and userspace system utils. It seems technically less "Linux" by this metric than Chrome OS and equal to Android.

I don't think this is principled really beyond the fact that Google chose to use different branding whereas FOSS distro vendors actually called what they distributed "Linux." Sort of how Hyenas are phylogenetically feliform but most people consider them dogs.