As I previously said, I'm not sure if Larian is still going for this backstory when it comes to Astarion, but this seems to have been the case for demo version back in Februray. Here is the full quote in regards to that:
" In this case, we were shown Astarion, who seemed like a real asshole. A disgraced nobleman who used his position as a local magistrate to serve a vampire clan by feeding them prisoners, he was eventually too corrupt even for them and was effectively sent to serve as the personal slave of a powerful vampire. Astarion has the affected sophistication of a true decadent, like one of Richard E. Grant's less likable characters."
I was expecting an evil background, so no surprise here, but I have to wonder however did he manage to