In his willingness to prove that it coulnd't be Dean, HIS BROTHER Dean, he'd forgotten about the pentacle tattooed on his chest that was identicle to the one his brother wore. Assuming that this version of Dean HAD that tattoo. So he went with the holy water bit. Better safe than sorry right?
Well, that would have explained a lot had he bothered to listen before spiking his beer with anti-demon juice. He knew about the whole pulling demons thing. Buthe hadn't started being able to do that until he and Ruby...
Okay. "Yeah, Dean, I really have no memory of the last few weeks here. I was wi-," he paused. He was not going to say Ruby. Dean would not like that so much. "Well, I was alone and you were dead. My last memory is of being in some cheesy love-motel themed craphole and then I woke up here." Yeah. Smooth. Real Smooth.