Have you ever seen a movie trailer that plays a flick up to be something it's not? How about an ad that gives you a totally different idea until they start talking about the product? It happens all the time and it's an example of how much power editors have. Of course it also shows how poor of a job many editors do as well, but that's not the point (and a subject for a different post all together).
I found this bit that displays how easy it is to turn something that's not a dating sim into the opening for one.
Suzumiya Haruhi (hoax) dating sim