Android devices run deprecated Linux kernels that have a bunch of proprietary binary blobs plopped onto them, so technically "Linux", but not an easily updateable mainline kernel like most people are referring to when talking about "Linux."
Debian is GNU/Linux and that's what almost always people mean when they say Linux. Android is not GNU/Linux and doesn't even use the mainline Linux kernel - just some old, heavily modified version.
Mobian or Manjaro ARM on the other hand are GNU/Linux distributions. They run the same software that you can run on your desktop distro.