I'm telling you this as someone who loves dogs, has 3 pits myself, and has a lifetime of being around different types of dogs breeds - this was both of y'all fault. The couple SHOULD NOT have approached the fence. If that google doc specifically said "has problems with other animals", I WOULD NOT even take the risk of letting it go off the leash. It would be on a tight leash the ENTIRE time.
I am sorry this happened to you, but I wouldn't be surprised if the dog would have to be put down now (it all depends on local laws relating to these kinds of things).