What are Pennsylvanian laws regarding hit and run accidents?

I was backing out in a parking lot very slowly and tapped the back of a car behind me. I came out the vehicle immediately to assess the damage and upon investigation I didn’t see anything that warranted any attention. The owner was nowhere around so, I left a note with my phone number and apologies. A week later I received a phone call from a law firm represented the vehicle’s owner claiming that my minor bump resulted in significant damage. I wasn’t even moving at a speed that could have caused any significant damage and suspect that the owner is trying to pin another collision on me. What are my options? Can this be considered a hit and run accident? Luckily, I took a photos of both vehicles before I had left, plus a picture of the not to establish a time line.