I'm with you.
We have an unknown person (A) reporting an incident, for which we have no corroborating evidence, passing along a license plate number belonging to another unidentified individual (B) to another unknown individual (C) via the internet.
Even if person A does nothing with the acquired information, person B's information has been disseminated anonymously with the impression, rightly or wrongly, that they caused an accident with a bike rider. Person C now has the option of doing with this information anything he or she desires.
And a license plate number only identifies the owner of the automobile and not the driver. Could be a car of a family member or friend (possibly of the same age and gender making identification even more difficult).
Wasn't another frequent A&S poster banned for some duration for a similar disrespect of an individual's private information?
If you're in doubt about an incident with a driver- call the cops- if you accept $20 and ride off, fine to share the story of the incident on line but passing along their license number to someone seems decidedly uncool to me.