I'd find out what constitutes the "one free bite" in your jurisdiction. If a report like this triggers your having to get special insurance, muzzle your dog at all times, put a roof on your yard, etc. - not to mention the spectre of him being taken from you and put to death if the man or someone else should decide to make a second accusation - then you need to fight it now.

If there has to be a judicially proved bite before your dog is tagged a vicious dog, then just collect documentation and sit tight, as others have said.