Lxc iirc.

So in the end what's important is if you're good enough for _yourself_

Android is technically Linux, sure. But it doesn't share the Linux ecosystem. GNU/Linux would be a way to distinguish, but it would exclude distros such as postmarketOS, which are part of the Linux ecosystem.

As someone who wanted to use 9front as a toy OS for a bit, this makes me excited.

For that you'll need to port Android to the RPi4 and then to this. Doesn't seem impossible though.