As far as I can tell they basically use the same technique for these other OSes like Easy Debian did: chroot into the userland of some GNU/Linux with a desktop. So they're technically not "booting" another OS. It's still the Android kernel booting, even if you see a Debian Desktop. This is also why you'll eventually run into this problem on the Gemini too: There will come a point where the Android kernel won't be upgraded anymore, and because Android isn't truly FLOSS, you won't be able to do it on your own. Then there will come the point where the outdated Android kernel won't be compatible with then up-to-date GNU/Linux userlands and you'll be stuck with old software you can't do anything about. Sounds familiar? This "vision of the future" is exactly what made me ask those questions in my first post of this thread.