Did they impound the PB? He should be observed for rabies.
I don't know how dog parks work where the OP is but by us you have to have a permit and in order to get that permit the dogs have to be vaccinated and up to date. But by me there would have been no fines either because it's states on signs as you walk in that they are not responsible for any injuries....enter at your own risk. When my dog got attacked the owner paid for the vet bills on their own and no report was ever made to anyone.
Misty- Samoyed Mix, Tannor- Golden Retriever CGC
Robyn- GSD CGC, TC, Midnite-GSD CGC,TC, Brennan-Golden Retriever CGC, Batman-Husky/Greyhound , Apollo-GSD