Revealing mistake: At the beginning when Michael has KITT move the truck, you can see the dolly apparatus that makes the truck's rear end swing out.
Revealing mistake: In the scene where two truckers try to smash up KITT with baseball bats, and KITT supposedly moves a bit backwards by himself, you can see someone 'helping' him near the passenger's seat.
Answer: I would say that unless there's visual evidence it was another K.I.T.T. car, as in you could see the bar scanner or cut steering wheel, people on here would correct the mistake by saying more than one 1982 Pontiac Firebird Trans-Am was sold and there's no reason it's meant to be a random car.
Bishop73