Why did she act like this towards me?

I left uni five years ago. Anyway, I was in a pub in central London last week and I saw a girl that I hung out with quite a bit at uni, who was also going out with a guy I was friends with from my course called Dave. We went clubbing, house parties etc together in a group loads of times, and although she was going out with Dave, I thought we were friends cos we used to chat loads and got on well and would always say hi and even danced in clubs together. Anyway they split up after uni so I hadn't seen her since. So I was excited to see her and went up to her and said hi, fancy meeting you here, what are you doing nowadays and she said she didn't recognise me. I then said we were at uni together and all that but she just said that uni was a 'haze', and that she "kind of recognised my voice" and then she basically turned away and rejoined her group of friends. I was shocked and angry. I can't believe that this person didn't recognise me or they could be so hurful.