GNU preaches free software. Steam is nonfree. I think they’re just trying to point that out.

I think what they were specifying was the role GNU plays in that sentence. Personally I don’t like calling one GNU/Linux and the other Linux, but the defining point of GNU is that it’s uses only free open source software, and does not contain any non-free (as in speech, not beer) software.

I didn’t the license did :)