Dean watched Anna warily. Would this be confession time from her too? Would she tell him that she had been one the "others" that had wanted him to torture Alistair? Only for him to get his ass kicked and stuck with tubes going through him? Luckily, Dean who seemed to have gotten good at shutting his mouth before blurting something out (at least for this night), said nothing. And as he said nothing, he did realize that it was fair. Anna would no more asked him to do that than Cas would have. In fact, Dean was damn certain that she would have been less likely. Because she still remembered what it was to be human and she was always on his side. That he believed wasn't a lie.
Still. Dean wasn't in the most favorable moods. This hadn't been a good night for him. So instead he asked, "How long have you been listening in?" Because just as Ruby had her ways he knew that Anna had hers too. Better ones likely.