[/spoiler] I'm just referring to the time you first find out hes a vampire and he states that he only drinks animal blood, I dont know if he was lying or something, [spoiler]
He is not lying about an animal bit, but he is about the reasons behind it. Which you can call him out on if you had DT activated.
He is making it seem as if he is feeding on animals by choice because he is not "a monster" or doesn't want to be one. In truth, he was forced to do it by his master, and him trying to feed on you is him testing out how "free" is he from his master now.
Also, since we are on topic in regards to Astarion. I recall an article that mentioned a very interesting bit about Astarion's life prior to vampirsim.
Apparently he was a disgraced nobleman who became a magistrate as just a cover. In reality he was smuggling prisoners to vampires. After he became "too corrupt" even for vampires, vampires ended up making a scheme with Cazador to take him down. Hence how he ended up enslaved by him.
Now, I'm not sure if this
backstory still stands for Astarion, or was it changed by now. However, if we do follow this, then in all honesty he is the last person to talk about the importance of being allowed to chose.
Since he was basically a glorified slaver himself before his downfall.
If this is still meant to be his backstory prior to Cazador, that is.