well its possible what ever he saw on you tube he wants that or his friend are pressuring him
but im 13 too and never experienced that
He was probably just joking. I am a 13 yr old girl with a 12 y rold cousin. He touches me like that and i know he is only joking ,doing what boys do! Maybe you should talk to his cousin and tell her that if she finds it uncomfortable then she should tell him to stop!!
hope i helped!!!