actually, i've never had a one nite stand, or even another partner--just my husband. so, i can claim whatever.
but, i'm also not judging anyone. i'm not saying that having sex is wrong in a general sense, but that it seems that she has certain expectations and that her boundaries were blurred a bit--and that's how she got hurt. I had a friend who went out 'for a drink' with a man whom she liked, and he was later seen at the same bar kissing some other girl. She thought they were 'on a date' and had that expectation. he thought they were 'going out to get a drink as friends' and he was free to meet people. So, she got hurt because her expectations and boundaries were confused. Had she communicated more effectively, or set clear boundaries, it's likely that she would not have been hurt.
i don't think the sex is the issue, and no one is a slut for having sex when they want to. it's how they feel about the act, why they do it, and what outcome it brings them as to whether or not a particular action is appropriate.
and, i hesitate to call a guy a jerk simply because he wasn't communicating clearly either. most people dont' communicate clearly; most people have blurred boundaries. The best thing to do is to get good boundaries and learn how to communicate. Then, you know what you want,, you know how to communicate what you want to another, and thereby you are able to recieve it.