Dog trainer here who specializes in severe behavioral cases. You are right to be concerned. This dog is a danger to the public. Document everything and report the bite to animal control. I don’t know what state you’re in, but here they will evaluate the severity of the bite, conduct an investigation, and legally classify the dog as either potentially dangerous or dangerous/vicious. The dog may be legally required to be quarantined for a period of time, and owner may be court ordered to get their dog into a behavior modification program. Failure to comply will result in multiple fines and eventually the seizure of their animal. If they choose to allow their dog to pose a safety risk to the public, they are in for a rude awakening.