Hmmm, I don't think they are one and the same... but because Astarion is my favourite character, I can't resist the lure of a good theorycrafting/character analysis thread.
So several days ago I mentioned while giving feedback that I think Larian is trying to pull a fast one and I made the prediction that Astarian is really..... wait for it..... waaaait for it..... Cazador.
1. Astarian is constantly seeking to control the parasite, to learn how to use the new power that the parasite is giving the group. Power and control are what True Vampires live and feed off of, other than blood. To dominate one's mind, actions, and existence is what they get off on. Vampire Spawn simply do not have that mindset as they are nothing but puppets as Astarian points out many times.
He wants to control the parasite because power and control, to him, mean survival. Let's assume that he is who he appears to be, a vampire spawn who was a slave, and now finds himself free. It makes complete sense to me that he would clutch at any bit of power that he can, to survive and stay away from his abuser. He has also likely taken on parts of Cazador's controlling personality as a mask to wear, because - let's face it - if he's only known someone else's power and control for 200 years, then to him, that is how the world works.
Also, have you heard his response to a certain dialogue choice you can make when you talk to him after your tadpole dream, when he first tells you about having been a slave, and you tease "I didn't know you had a master in the bedroom" or something to that effect? Holy crap. Normally he enjoys cheeky responses from your character, but his response to this in particular was so angry, so hurt, so well-acted that I had to re-load my previous save and NOT choose that option again! He may be secretive/evasive about some things, but his responses about having been a slave and having been abused are very telling, especially in this scene. I certainly think his story is exactly what it appears to be.