CM is not Android, it's AOSP-based. Android is closed source but it's very similar to AOSP. Same goes for Chrome/ium and Chrome/ium OS. You can indeed say that

CM is not Android, it's AOSP-based. Android is closed source but it's very similar to AOSP. Same goes for Chrome/ium and Chrome/ium OS. You can indeed say that most mobile users are on a proprietary OS and most desktop users are on a proprietary browser.