It's becoming something of a trend for them to have two - Avengers itself did as well, I think? Or maybe I'm misremembering that. Anyway, having read Jens' review beforehand, I stayed for the second (but I admit the credits after that first post-credits scene were nowhere near as fascinating as the initial ones...).
Anyway, what happened was basically just Jane moping about how long Thor would stay away - and then storming outside to the terrace as he appears, and the scene closing on a passionate kiss. And then a fairly hilarious short shot of that monster brought into London during the earlier fading of borders between worlds, bowling over cars in a deserted carpark and looking surprisingly like a cute but semi-lame dog.
Certainly a valid argument. Well played.