Is my sister's son autistic?

Chances are that he is considered a hyper active child - one who has been overexposed to things which should not have, like the TV. Only channels with parents guide should be allowed. I also think nobody punishes him or communicates with him seriously - shouting is not communicating. Both his parents are very pampering. You and his parents have to be strict and serious with him. No is no. At least you do it when he is around your daughter. All the best.