I dont doubt it is possible that he owned this car but highly doubt it was used in a photo shoot for the first movie. I dont doubt he was told such either as I have heard personally from other involved in the movie says things like "Bonnevilles were used for the Sheriff car." Things do run together after so many years. That car should bring good money, just wish more pics were shown and the title with name for sure proof.
Would Burt have painted that car with "Bandit" on the door prior to the 2nd movie for a photo shoot? Can you tell by the T top opening in that prop pic if that is hurst or fischer tops, my eyes are not that good. Would be a tell tell sign if that is the same car as we know the 2nd movie had fischers.