There seems to be no dispute that the damage was there when the car was returned
As mentioned, it doesn't matter how the damage was caused, you are accountable for any damage found on return that wasn't noted when taking the car 00

At the moment, I would wait and see how much Hertz bills for the damage and itemise what it relates to

If there is a small scratch and it claims several days loss of use cost, that can be challenged

If you have coverage that will help you ( e.g. insurance or a rental car cover ) I would contact it in regards to making a claim

You may well not be responsible, but you are accountable for the damage