Little boys!!

It is our town days! We spent the evening watching the pulls. Where a friend came to join us after she spotted us in the crowd. She has 6 year old boy and 3 girl. Our daughter was sitting very nicely in her wagon. When her little boy came over and started hitting her for no reason. I asked to stop which it did for a second. Few seconds later he started hitting and choking her again. His mother didn't even step in to discipline him at all. My husband and I had to keep telling him to keep his hands to himself. He would get up and go whine to his mom that he was bored and wanted to go and would come back and start hitting our daughter all over again.

Are all little boys like this? We're having a boy and I am now terrified to have one. I don't want him to be so aggressive or mean to other children.