Everyone drives drunk, I don't mean 20 beers deep lets go driving. I mean, he had a small handful of shots at the beginning of the night, and a few beer after that, and this was early in the night. He left before the sun rose, but he wasn't noticeably drunk when he left.
It's a good thing he didn't, or else there would have been ambulances, police, and a fuck ton of trouble for the grad class the days after. It ended well, and they learned a lesson.