Please tell me if I'm overreacting?

I'm watching my nephews today and they are normal kids. They get wild at times and have fun and as I see it they are just normal. They had a friend over and they were looking at stuff on Youtube and the friend pulls up something that he and his brother watch all the time. It was, what I would call, extreme nature, I mean horses doing...... The friend was saying some rather nasty stuff, I won't go into that. I will say that it was so nasty and uncalled for that it made me think he has some issues and will have more as he matures. He's only in the 3rd grade.He didn't know I could hear. When I looked over his shoulder I grabbed the laptop, closed it and the friend said, "Hey, I was using that!" I said, "I don't give a damn!" He placed his hands over his ears and said, "Children in the room." (bratty) That's when I said that children shouldn't be watching this and making comments like his.

My question boils down to this.....

Should I tell his parents? I think they know his behavior. I don't think they care. Am I overreacting or is this normal for some 7 year old boys. It's not normal for my nephews, I know that for sure.

I'm just disgusted and can't get over it.