He shouldn't have slapped his Mum but his Mum was no better. She shouldn't have elbowed him and do the things she did to him, it antagonises and provokes him, making matters worse.
Being the Nostradamus-in-training I am, there'll be a video posted in years to come, where we find out he's got some kind of special needs (ADD/ADHD, etc) and is taking anger management and is on meds.