"Ahh. I'm sorry. Thought you were another new face. Just started tonight myself. Haven't gotten an assignment yet, though. That'll probably be in the morning." That's a good way to explain the suit, right? A job interview? It makes more sense than what really happened, so let's go with it.

"I hope you're having a good time, though. And I really am sorry I thought you worked here." The smile turns a bit sheepish as he tries to apologize for his mistake.