Why did this happen, why was this kid so rude?

My mom was outside giving me a hand and this kid on a bike came up to us (he was about 11/12), and said she was an old woman and told her to 'get back inside now!'. He also told her to move from where she was living. I am absolutely appalled at this. He talked to her like she was an animal. What are you supposed to say to a kid of this age when they are rude like that?