I have been out of the US for damn near 10 years now, so I may be unfamiliar with the laws in the Carolinas.
With that said, in some states that is not true. I have watched enough COPS over these years to know and have heard the police say many times that "someone has to take a ride downtown"
In short, if there is a report, regardless of whether they are makrks or bruises, the law in some states say that at least one party must be booked. The officer must decide which based on what he/she hears...but yeah. Again, Im not sure in NC/SC are one of those.