It's not clear what you are curious about. You can run GNU/Linux with out of tree modules (e.g. proprietary nvidia graphics driver). That doesn't change the fact that you're running a (now probably tainted) Linux kernel.
I don't think anyone is thinking of a GNU/Linux desktop environment when they think "Android runs Linux!", they are quite literally thinking "Android uses the Linux kernel." They are not wrong.
I don't think anyone is thinking of a GNU/Linux desktop environment when they think "Android runs Linux!", they are quite literally thinking "Android uses the Linux kernel." They are not wrong.