She fukked up not nipping it in the bud when he was younger. Folks don't realize that your parents are your first teachers, not the ones you get in school. Yes, kids act up in public, but this is a case of bad parenting because his parents should've taught him how to act in public. Not even in public, but you shouldn't be putting your hands on your mom period. It shows that he has a severe lack of respect for her, but if you don't instill that day one, good luck tryna do so when he gets older. shyt my mom would've whipped me in front of everybody for showing out. Lord knows what my pops would've done once he found out what happened.
Sad thing is the kid might have a disorder, but you can tell she spent years pacifying the behavior instead of addressing the situation initially. I've worked with kids who displayed the same behavior and a lot of cases unfortunately (not all), the parents don't get their kids the help they need because they pacify the behavior for the time being hoping they child grows out of the behavior. Alot of times they don't want to be seen as a bad parent due to what society tells you on how to raise a child as if every kid is the same smh. Or they flat out don't accept that it's a problem until it's too late.
Judging by her reaction. This isn't the first time this happened. She doesn't know what to do.