When I finished talking with her, I told my friend about what we talked. I also said to him that I made a little joke with her. He didn't ask what joke it was, so I didn't tell him. I figured if she would say anything to him, I'd explain him it was a joke.
It turns out that she stopped contacting him. He noticed this and asked her what was going on. She said she had stopped contacting him because I had said to her that I'm his girlfriend. He denied this. He said to her I'm just his friend.
Today he told me he had talked with her. He asked why did I introduce myself as his girlfriend. I said I only made a little joke. Then he got mad, called me immature, and called my joke as inappropriate.
I don't understand why he would take it that bad. Did he think I like him for saying that?