Things like this happen everyday. It may seem bad to say, but there's really no way of tracing you down or the other car. There are many cars in a parking lot passing by or parking around a vehicle that can cause minor damage, or it could have been the car rubbing against a concrete barrier.
The owner of the other vehicle might just look at it and shake their head, "When did this happen?" and easily fix it with touch-up paint.
No need to report it to the collision reporting centre - doesn't meet the damage threshold as you correctly pointed out.