Calling ChromeOS Linux is like calling Android Linux. It's barely passable in that it derives from it, but there are so many things different.

SteamOS has the benefit of being basically entirely open and modifiable. Heck, it has KDE Plasma for its desktop mode.

Android is Linux, just not GNU/Linux :)

Yeah, the GNU disambiguation is relevant now. Years of interjecting for a moment have paid off.

Yeah, except for the whole steam part of it, which includes the input stack. You can build far more of ChromeOS from open source than SteamOS.

For now, you can draw the line for what he means at GNU since SteamOS is that while ChromeOS is not. But if someone made a GNU/Linux that holds your hand everywhere like ChromeOS, it would probably be "not real Linux." So maybe the better designation is "Linux for nerds."