Surely there would have been signs at the exit from the car park to indicate that he was entering a one way street? Also if he'd parked facing the wrong way wouldn't that mean that he had just driven the wrong way, either to get in the space or to continue when he left the space?
Anyway, I thought if you drove off before the ticket was written and before they slapped it on your windscreen there was nothing they could do about it...but maybe I'm wrong about that, I'm only going by what I saw on that prog that used to be on the tv to do with traffic wardens in London.