He DID recently swing by Blake's place in the Horizon, which I understand is next door to Crane. There might be something to that, maybe Crane spotted him during the exchange and is Curious enough to approach Dean about it?

Alternatively, Dean's got his own house and isn't at the inn as often anymore, but after Jesper's announcement today it's very feasible he'd start coming around to scope things out and prepare for the remodeling plans! He could be there drinking kinda late and see Crane come in at a stupid hour and be like, "Long night?" suspicious squint.