Hit a car with my door - no damage?

Hi! Looking for advice on the likelihood of a claim to my insurance, and what I should say should insurance companies send me an accident form.

I was late to pick my sister up from her tutor, so i parked in between two other cars. In a rush, I opened the door and accidentally softly tapped the car next to me. I quickly glanced down and saw no damage. When I looked back up, the driver turned around and looked at me, where I mouthed 'sorry!' and held up my hand, indicating for them to wait so we could sort out the issue.
At no point did they attempt to get out of the car, to try and talk to me or indeed to follow me towards where I was going, which I'm sure they could see as it was well within view of both of our cars, and one would assume they would be watching where I was going.
As I was waiting for my sister, I saw a woman look at the side of the car and then my own car, with a notebook in her hand.
5 minutes later after picking up my sister, the car was gone.
I presume there will be a claim to my insurance for this, as they will have written down my number plate, but what should I say? Any advice whatsoever would be very helpful