Linux is really only a thing because it ISNT Unix (which macos is). Theyre more related than windows because they're both POSIX compatible, but share essentially no codebase.

A rooted android phone on the other hand is just plain ol linux compiled for ARM, with some custom google jazz. It utilises a lot of Linux components like cgroups and SELinux - commonly found on desktop Linux (especially with containers).

Its not really that important in a broad sense to be honest, but it definitely makes android a Linux distro.