Why She Says "Nothing" When She's Clearly Upset

I was on a snowboarding trip and while in a cabin with a group of friends, I found myself talking to a single 34 year old man who insisted that women are confusing. He said if he asked a woman what's wrong and she said, "nothing," then he would just leaves her alone and that would make her even more mad. I told him that's exactly what he's not supposed to do and that there is a right thing to do in this situation.

So why do women say "nothing" if they're clearly upset?

In a guy's mind,