Good thing you left there - protecting your daughter is the best thing to do in that situation. I hope it wasn't too serious of a incident .
The other family will have to deal with their own problems, probably soon it sounds like. I hope they will see soon that their boy needs some boundaries or an evaluation even. Are his sisters older or younger?
Sometimes it can be innocent curiosity if kids are close in age, that was too much of an age difference for that excuse.