Exactly. Proton is Valve’s name for their WINE-based product. It’s basically WINE with some patches to work with the Valve ecosystem.
It’s also largely community driven, but that didn’t make it not a Valve product, Valve still controls what goes in and what doesn’t after all (which is why projects like Glorious Eggroll’s proton builds are so prevalent, sometimes you want to try stuff Valve hasn’t approved yet).