To me, it does make sense that Astarion thinks our Tav is in league with the mindflayers who captured him: It is implied that he saw us walking around the nautiloid while he was still trapped in his pod. Before some of the pods were damaged, the cultists we encountered were the only ones who could roam freely, aside from the mindflayers. So I think it is quite understandable that he assumes that our Tav is also a cultist, and should know about the parasites. Unlike Gale, he does not know anything about tadpoles and ceremorphosis, so interrogating a cultist would make sense.
What makes little sense, then, is that under the assumption that you are one of the bad guys in league with mindflayers (except he just saw you killing other intellect devourers, by his own admission, but ok...) it would be a clever idea LURE US into making a kind gesture for him.
Then again, admittedly I'm not as terribly offended with Astarion daring to bare his fangs at me, the holy Protagonist, as some other people seem to be.
No, I have to admit I'm rather growing to dislike Astarion far more for the type of person he's proving to be on the long term, rather than for the bad first impression.
So far, I think he's the worst character in our party by a landslide. The other companions may be reticent, opportunists, single minded or what else, but no one comes close to it in being gratuitously mean spirited.
He's a whiny hypocrite that thinks it's incredibly amusing to mock, punish, kill or and inflict gratuitous suffering on others, but at the same time becomes incredibly touchy and melodramatic when he's the target of any of the aforementioned.
