I think you are spot on in your thinking that this is to get you to change your mind, they love a bit of control (sweeping generalisation). Taking positve steps by changing his behaviour is too much like hard work, bullying is easier.
My exA is threatening to report me as an unfit mother to social services (they aren't even his children) It worried me for about a minute!!!!! One of the reasons I wanted him gone was that I didn't want them exposed to his crazy behaviours