Aziraphale matches the coldness of Lucifer's expression out of some terrible combination of instinct and pride, though internally he is absolutely panicking. He feels the air go out of him a little at Lucifer's response - now you've done it, you've pissed off the Devil - but Crowley's interjection, his insinuation into the situation and almost between them, in fact, is even worse. Aziraphale bristles a little at being explained, apologize for, though he knows it's the only sensible course of action Crowley has, some part of him remains wholly nauseated by the whole ordeal.

"That is what I meant," he agrees, desperately quashing down his desire to continue making an absolute ass of himself. "We are... not related. Different universes, cosmologies, that whole... bit."

He refuses to actually apologize, or to acknowledge the mention of his 'manners'. Aziraphale will be only as polite as he has to be to survive this meeting, and not a jot more.