Why is my supervisor giving me a cold treatment / being possessive? What should I do?

I am a student working on a thesis with him. At this conference, someone introduced me to a potential recruiter. We start having a chat (in a group of 4) when my supervisor walks into the conversation, and then apologizes for interrupting. He never does this usually, so I am thinking that he sensed something. He then left, and the recruiter, myself and the person that introduced us moved to a different area to discuss the possibility. Later, guy that introduced me and I walked towards a lecture room, from where my supervisor was leaving. He barely said anything + accidently slammed into someone else.
For the rest of this conference (a 4 day event), he was acting odd and ignored me completely. The night that this happened, we all went to a party where he didn't even say hi to me, and so I also ignored him completely. Am I in trouble and why is he being so possessive?

Additional Details
Not married or interested in him. Just don't know where else to post this question...suggestion

Thanks Mafasiou

Your supervisor wasn't be possessive. You know what possessive means? This supervisor was acting on impulse. He assume you were being accredited for something that should have been addressed to him. Next time place this in another catergory like business.

I already answered this question. If he has something to say he will say it. What has happened has happened. No sense worrying about it now. It is his problem wouldn't you say? You are young and will find in the work place there are just some people you will never understand. Focus on your own goals and let others worry about their own issues. If you haven't done anything to feel guilty about, then don't.

you should sleep with him or either he just wants to sleep with you and don't know how to ask-just kidding but he's your supervisor so who cares? As long as you're doing everything you're suppose to be doing and that paycheck is right then that's all that matters. Otherwise you may have a harrassment suit on your hands.