Castiel is an angel. He didn't expect to have a soulmate, but yet here he is. He'd discovered he's had your name on his shoulder in every vessel he's had, and now that he's in a grocery store for whatever reason, he heard you introducing yourself to someone. Which lead to now. "Hey, uhm... I think.. We went to college together?" This was stupid. That was a lame introduction, because he knows it's not true. But he's desperate, and it was the first thing he could think to use.