Don't listen to everyone else. It is obviously the fault of everyone but you. That choker collar manufacturer is obviously at fault for not warning you that a strong dog could break the collar. Everyone in that park should have been warned by the park management they shouldn't walk their pets anywhere near your dog that looks like a pitbull, but isn't, therefore it is on them. How dare someone bring an 8 year old and their dog into a park where you and your dog are clearly the top dogs, that is totally on them. And isn't there anyone in that park that can stand up and talk to you, man to man? Why should anyone want the park authorities to handle a situation? Someone has a problem with you and your dog they should have come over, stood face to face and told you what they thought. If that escalated and something untold happened, hey it would be their fault for bringing a knife to a gunfight.
I would have had the police come and take statements because it is quite clear this isn't over. Any dog attack in my parks is not going to be ignored. Such an incident would put any dog owner on very thin ice and your attitude clearly would have broken that ice, so you and your not quite a pitbull would be out.