It does not sound like your friend's dog is repeat offender or viscous. So, it might be wise to avoid a rush to judgment until they have spoken with the city or county attorney responsible for bringing such a case to district court. Usually the city or county will not seek to have a dog designated a threat or viscous dog for a first time offense, especially if it is more of a correction than bite (quite a few working dogs use a nip to direct livestock or deter certain kinds of behavior). We had a Border Collie that would nip or use a correctional bite on anyone who moved too fast (this included us). Quite often people telegraph the wrong messages around dogs too (they act suspicious or scared - both cues dogs pick up on as problematic).
When I was kid, we had dogs running loose everywhere. They were neighborhood dogs that knew everyone and were typically closely bonded with neighborhood kids and their parents. The only dogs who bit anyone where those dogs that were constantly chained up and never allowed to socialize.