To the extent that Linux implies "GNU Linux", i.e. a whole operating system and a broadly interoperable and source compatible set of *nix services, Android is not Linux any more than iOS is FreeBSD.
RMS believes that userland makes an OS, because he wrote a userland. Linus believes that kernel makes an OS, because he wrote a kernel. Calling Android "Linux" is like calling Windows 8 "Windows NT", i.e. correct if you're talking about kernels and wrong otherwise.