The last part is rubbish, the land might be privately owned but it is open to the public and therefore for traffic purposes an open road and all traffic laws apply.
Unless there was a witness then it's unlikely anything will happen, given that the car you bumped into (if you did) is long gone I can't see how you can do much more about it.
Personally I wouldn't worry about it at all. The fact you didn't notice a bump would suggest to me somebody hit you rather than the other way round.