Strange Situation in Hallway at School. Why Did These Guys Do This? 10PTS?

I'm a girl, 21, taking summer courses at my university atm. Last week, after classes were finished, I was walking through a hallway (on my way home) when a group of tall guys (maybe 4-5) were walking in the opposite direction towards me. They looked me over as I past them and then one of them suddenly grabs my arm and says "hey, you remember me, don't you?" These were all strangers so I was really frightened and said "no" (obviously). The other guys were saying things too but I just remember freeing my arm and walking away really fast away from them. I still heard their voices close by shouting at me for a bit and actually feared they were following me. But I didn't want to run and cause a scene since the hall was not empty. Luckily, they didn't follow me but honestly, I've never been so afraid in public in my life, like just the fact that that happened in a hallway with other ppl makes me really uneasy. Am I over-reacting? What should I have done? Or, what should I do if a similar situation occurs in the future?? much thanx.