Why don't you ask HIM? We don't know him or you so we don't have any idea. He could have been just teasing her. Hard to say. If you want to know why someone said or did something, ask them. Easy-peasy.
A guy that I last saw when I was in 4th grade, went up to my sister and told her that I was his girlfriend. Is he interested or was he just joking? Please help!!!!
Help? To understand what someone meant by a comment made? ONLY that person will know what they meant by it .. You will have to ask him, if you really need to know.
Personally, I would ignore it .. But, that's just me.