That’s the way I understand it, though I don’t have an education in moral theology. Anger, for a just cause, is not the sin of anger, but of judgement. To not be angry, when there is a just cause to be angry, may be a greater sin (i.e. silence is acceptance). However, instead of listening to me, I would suggest talking to your priest or contacting the diocese and discussing this with someone who has a degree in moral theology. Perhaps, they can explain it better and correct any misinformation I may be giving.
CCC 2302 By recalling the commandment, "You shall not kill,"93 our Lord asked for peace of heart and denounced murderous anger and hatred as immoral.
Anger is a desire for revenge. “To desire vengeance in order to do evil to someone who should be punished is illicit,” but it is praiseworthy to impose restitution "to correct vices and maintain justice."94 If anger reaches the point of a deliberate desire to kill or seriously wound a neighbor, it is gravely against charity; it is a mortal sin. the Lord says, "Everyone who is angry with his brother shall be liable to judgment."95