If anyone's wondering... expect some INSANELY INTENSE snusnu once they're at his place (well, she'll pass out first, then after she wakes up, she's gonna be dicked good and hard LOL
What he's saying is theoretically true. They have broken up and she should not have to explain anything to him anymore. If he wants to misunderstand something, that's his problem. And the best course of action would be to take him to court.
But practically I don't think that is a good idea. A guy who turns up at your office after a break up, can and will cause problem. Deescalating the situation while making to breakup clear should be the priority. You should not be giving them reasons to get angry. This could be dangerous. Also, it might be easy for him talk about lawyers but normal people don't think about suing immediately because lawyers are expensive.