Oh right, that's more reassuring. I guess you'd still have to cut a deal with Valve to use FPs fork commercially though? Which is a wildcard since the licensing terms aren't public as far as I can tell.
I doubt its much of a deal. Garrys Mod and Rust have both been wildly successful (which means Valve has made tons of money off them as well)
My point is, if I were Valve id let Garry run wild with my engine--no deal needed. Hes proven himself more than once. Just a thought!
There is already a deal between Valve and Facepunch. I don't know all the terms but you will need to publish your game to Steam (not exclusively).
https://sbox.game/dev/doc/systems/game-exporting/ (bottom of page)