This happens all the time, if for example a car opens a door and hits your door and leaves a mark you do not need to confront the other person. Get their reg number make of car and report it to your insurance company, they will then initiate a claim against the other party’s insurance company. Most of the time this will be paid with no problems, I would say someone has had something done to their car and they have taken your reg number and reported it.
if you are sure you have done nothing wrong tell RSA under no circumstances are you to pay the claim and that you have reported it to the police as insurance fraud.