Chrome OS is a variant of GNU/Linux. Android isn't, it only has Linux kernel, but the userland is mostly incompatible with any existing GNU/Linux distros (there is some resemblance, because of *nix roots and POSIX compatibility, but not much)
That's why I said the traditional Linux desktop. Android uses the Linux kernel, but has a completely different stack on top of it. Also, more and more functionality is moving to the proprietary Google Play Services and proprietary Play Store apps. Chrome OS switched away from X11 and is just a system that boots to Chrome for the average user (and its normal use case).
(Yes I know that you can switch Chrome OS to developer mode and install Crouton.)