My point is that Source is, itself, a game engine, same as any other engine. Many people associate Source with Valve's first-person shooters, which do all, for the most part, have similar movement physics, jumping physics, weapon physics, and... you know. Valve's games have basically been cut from the Half-Life 2 mould for the better half of a decade now. But Source is used for all kinds of games, it can be tweaked to do... well... anything other game engines can.
I understand there is, colloquially, a difference between "Source game" and "game that runs on Source," definitely. Just needs pointing out, sometimes, that just because an engine is so often used for similar products, that does not mean the engine isn't versatile.