Astarion couldn't forget what John saw during the flood if he wanted to. And he does want to.

"Thank you for your benificence," he says sweetly, briefly turning to him to offer an exaggerated, sweeping bow. "However, I am already extremely good at disliking things and people, and I still did not need you to show up and underline the fact that the two of you had already made a decision on the small matter of whether or not I can be forced to serve."