Anger is a normal and healthy emotion, it is not the cause of abuse. Many people get angry and never engage power and control, many people who use power and control in a relationship are not angry when they do so. When abusers state they act in an abusive manner because they are angry, they are refusing to take responsibility for their actions and their choices. Rather, they choose to blame an emotion and deflect responsibility for their choices.
You are not responsible for your partner’s choices, only they can be responsible and take control. To state anger is the cause of abuse places the responsibility on the victim, blaming them for causing the anger and therefore, somehow, being responsible for the abuser’s actions. This is never the case.