Board Thread:False Info and Speculative Discussion/@comment-11260666-20140326163647/@comment-7938388-20140328091832

I'm pretty sure they wouldn't have Derek come back to town and not fill him in with what happened, even if it is off screen. They trust Derek.

Also, that scene is perfectly logical and it was also a way of the writers saying "Goodbye" to Season 3 and more specifically, Season 3b, finishing it off with the problem that started it. It's logical. You may consider it fan service just because Stiles is there but Stiles is the one who said it first, it would be idiotic for them to put Scott there saying it instead. The scene makes sense.