I'm pretty sure that that only applies to steam keys being sold on other sites. If it's being distributed in some other form, it can be cheaper.

This “most favored nation” clause in contracts is huge! It means that even if another store takes half of Steam’s cut (say, 15% vs 30%), the game can’t be sold for less, meaning other rival stores can never compete on price. In other words, Steam drives up prices for games economy-wide. Amazon does something similar, and this was part of the basis the FTC’s antitrust lawsuit against them.