Is it ok if a guy kisses my girlfriends hand?

So tonight my girlfriend and I, along with some of our friends went to a huge music festival here in Wisconsin called Summerfest. Anyways, as we were watching one of the bands play this guy she knew from high school came up to her and took her by the hand and kissed it infront of me and then said in a seductive voice "hey, how's it going?" Should I be upset about this? I know that if it was the other way around my girlfriend would not like that at all. I tried to play it off and introduced myself to the guy and told him who I was and he apologized right away for doing what he did, but my girlfriend has a tendency to be naive when someone is making moves on her, and doesn't react quick enough in those situations. She just let it happen, didn't pull away or anything. Should I be worried that things like this could happen and it could escalade with kissing on lips etc in the future? or am I being to uptight about the situation?