To be fair, if it was a baggage tug and towing a snaking line of baggage carts then if it 'grazed' the aircraft it could have been very hard to tell from the cab if contact had occurred.
As an airside driver I give them the benefit of the doubt as there arent any real details coming to light at this time.
However IF the two in question knowingly didnt report an incident then thats a different story. Release the hounds....