She was pushed too far.
At this point, the woman could feel herself getting angry, and even the man's wife could see how upset he was. Both of them were wondering why he couldn't just drop it. Even though they sat two rows apart for an hour, it wasn't a big deal. Any way you look at it, the mother made it clear why her son shouldn't give up his seat. She didn't have to change anything for this, and her son was staying put.
She tells him off.
The woman had had enough at this point. She pulled out her mother bear's claws and told the man to stay away from her and her family “Look, did you pay $100 more to get a seat that was already taken? No. Everyone has the same chance of getting their seats reserved.” She didn't want to talk about numbers, but it seemed to work when she did. The man finally changed the subject after saying a few choice words.