Yeah, and chromeos is more than just the chromeos used on chromebooks, it's also the Container-Runtime Optimised OS (CROS) and used for some other things too, it's "the google Linux".
I'd be speculating but I think inside google there's two Linux's, one which is the immutable OS built via blaze, more like an appliance, and the other is the "dynamic" user environment stuff based on Debian, that is intended largely to be throwaway in most circumstances.
(Chromeos is based on gentoo)