She's not right in any way. No, it's not cool for the other kids to have to watch his son eat and not have any other food, but the way she went about this is all wrong. For one, she has this sense of entitlement like it's his responsibility to take care of her other kids. It isn't. Second, she could have had a grown-up conversation with him, explained her side, and asked if he would consider the other kids sometimes when he brought food over. She didn't do that. Instead, she tried to create some gotcha moment and went at him completely wrong.
In the comments on the video, people are calling him petty. How? We don't even know that dude's pockets. Who said he's got the money to be paying for meals for 3 kids that aren't his every day?