@edelgard
Basically, the father is a genuine psychopath and the son isn't. The son could have some sociopathic tendencies based on the way he was raised but it can also be that he's just incredibly dissociated with a lot of events that don't concern himself and the ones that he genuinely cares for. I'm assuming that maybe he thought that his dad was similar to him in a way, and not just "inhuman" but he knows now that there's no difference between his dad and the monster in the driver's seat. They both don't feel what normal people do, which is genuine human emotions such as love and fear.