Thoughts about our fight?

My guy & I grabbed breakfast this morning & everything was fine. He needed to get an oil change so we stopped by the car dealership. While he was speaking with the mechanic, I walked over to the waiting area. One of the guys who works there started chatting with me. I found out that he attends my college & we are both trying to get into the same program. We were discussing entrance exams & campus preferences. So my bf comes over & puts his arm around me & rudely ushers me away in the middle of a convo! He was quiet & giving me one word answers from that moment on so I texted him later on asking what was that all about...

He never replied back. I mean....is this a normal reaction? I'm kind of turned off by how he reacted. I've not seen this side of him in the 5 months that we've been together. We're grown adults. I truly did not sense any flirting. We spoke all about the med program.