RVing w/ Pit Bulls

We have a pittie/american bull dog mix. We just check in advance to make sure he's welcome, I can always spend my money at a campground where he is. We also make sure he's always on a leash because you run into people who are nervous of him. I wish owners of other dog breeds would leash their dogs as well. We were camping over Memorial day and had two unleashed dogs wander into our campsite. How do I know if they are friendly and if one had attacked my dog, which one do you think would have been blamed?