Change of mind after accident

Hi, can somebody please help. I was reversing my car very slowly next to a parked car. The owner, sitting in the drivers seat claimed I caught the rear of their car. It was dark but we both checked the car under a light and there was no damage. No details were exchanged and we both happily went on our way. Two days later the driver has informed me there is slight damage and the car is going into a garage.

Where do I stand if they ask me for my insurance details or if they go to Police?