Most Helpful Girl
Not an issue. My boyfriend occasionally hugs mutual female friends of ours and that doesn't bother me at all. We might sometimes run into a girl or two that I don't know, he'll hug them hello, and introduce us to each other. Usually I know who they are and their relationship to each other already once I'm told who they are, and he introduces me as his girlfriend. So I'm not concerned at all. Very rarely do we run into any girl he knows that I haven't already heard anything about, and generally he doesn't hug them. I'm secure in our relationship, we don't hide much of anything from each other.
Most Helpful Guy
That would be a pretty extreme reaction, if I had a girlfriend and she reacted like that it would definitely present a red flag.
Granted I don't hug a lot of people, I wouldn't want my girlfriend to read too much into it.