Valve's interest is in selling the Steam Deck handheld, which is an Arch Linux PC that just defaults to a friendly console UI, playing Windows games transparently through Proton. It's probably the best example of average consumers using full-blown desktop Linux.
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."
I can't say enough how much of an advancement to Linux gaming Valve and Proton has been. The fact that I can pick up my steam deck and play 99% of PC games flawlessly is amazing compared to the state of Linux gaming a decade ago.