Physical & Emotional Abuse Support Group
Abuse is a general term for the treatment of someone that causes some kind of harm (to the abused person, to the abusers themselves, or to someone else) that is unlawful or wrongful. No one deserves abuse, period. Abuse can be emotional, physical, or sexual.
First. He went to anger management class because he couldn't see anyway out of it at the time. He is now using his attendance at that class as a weapon to club your sister over the head with. He never made an effort, at best he paid it lip service, at worst, he found a new tool to use against his family. How can you tell? Look at what he is doing now. He isn't managing any anger - he is exerting unhealthy control over your sister.
Second..although abuse generally manifests itself as anger, it is really about control. Screaming and yelling and cursing generally gets them what they want, which is dominance over others and the complete and absolute supplication of another human being's heart, soul, body, mind. That is what he is getting by constant demonstations of anger. That is also what he got by going to anger management classes. Your sister quite probably cut him some slack and gave him more than one break because he did that. See what I mean? It is just another tool in their bag of tricks. It goes along with sarcasm quite nicely. "I did what you wanted and you are still not happy so now I am going to do what makes me happy and you can just live with it". That generally is the mindset. He never intended to go, never intended to change. He just wanted to shut her up for a bit and clearly it worked.
When I was married to my ex it was his anger that I feared the most at one point, but what was actually more dangerous was his silence. When he was just in his head and not talking. That was generally when I was raped by him. There were rarely words involved, just actions. It had nothing to do with anger, he was exerting control in its most debasing and dehumanizing form.
If you need a book try Men Who Hate Women and the Women Who Love Them.
He is not using any of the tools he should have learned there and now he is actually using the mere fact that he went as another tool to control her. Emotional abuse in my opinion is more about Control and Ownership of another person than anger. Anger is just the best way to frighten someone into submission.
Sounds like he's a bully and a lazy one at that.
Your intuition is correct that he "Appears" to have made an effort. Thats what he wants, to appear to have done something right without actually doing any work.
If he changed his behavior towards her, he would no longer have control. It is rare that an abusive man can give up this kind of control and if he is still using the abusive sort of language that you describe it is obvious that he has not and is not willing to stop abusing your sister.