There's letting it go on and creating a big public scene like this, then there's putting that man in his place right then and there in the chat - stopping it from going any further. Thinking there's just something wrong, and that's all it is, negates the meaning of this going public.
I'm not saying that making this public was wrong, I'm just defending the other viewpoint, because I feel it's appropriate.
This doesn't really take into account the emotions of the harassed at the time does it? We don't know her motivations or reasons for not instantly telling him off and frankly they shouldn't matter because this behavior is completely unacceptable anyway.