Well, a whole lot happens in just a couple of seconds, and one could blame the wine for Aziraphale's prolonged, confused pause. His idly thoughts of times past and reminiscing over old human friendships is suddenly put to a half, and he watches Crowley move about in a way that far too obviously spells that there's something else to it.

He might not know everything that's going on in the demon's mind, but even the angel can't miss it when it's that obvious.

"Proposition-..." Aziraphale trails off, having pulled his glass out of the way as Crowley moved to refill his glass like the world may end if he didn't. Of course, the meaning is rather clear, and it does pass the angel's mind, but...perhaps there's an active choice in considering it might mean something entirely innocent.

(Are they still having a lovely night?)

"What do you mean?"