The whole scene makes zero sense. It was utterly ridiculous that Astarion thought he could distract what he believed to be his captors by getting you to attack the very same things that had taken him captive. It only gets worse when you decide not to help him and he says I was hoping for a kind soul....really?! You were expecting the monsters that kidnapped you to be kind and helpful? I really hope they decide to redo the whole scene it just doesn't work and ends up breaking ones immersion with how out of place it feels.
lol, i didn't even think of that aspect of it. You're right. It's ridiculous that he's playing the innocent "please help me against the mindflayers" to people he thinks are mindflayer thralls lol. I'm sure someone will say it's all part of his brilliant plan (lol), but I just don't see it.