You could say Android is just Linux ... but it's vastly different than any Linux desktop distro. It's got it's own display system (no X or Wayland), it doesn't have virtual consoles, the entire underlying filesystem layer, bootloaders and system drivers are entirely different. It still uses SELinux and FUSE, but in vastly different ways than a desktop OS.

I've never touched ChromeOS, but I imagine it's equally different. It seems like FushiaOS died off?