"This isn't just about forgetting to use hand brake as clearly the car was left in neutral rather than in gear. How many owners (or their hired hands) of cars of that caliber are that careless?"
Not sure exactly what David is saying. I'm not sure that the car was left in neutral ... could have been, but I do not know what transmission/drive train is in this Packard. I'm not an expert on the different types of "free-wheeling" that MAY have been used, but Packards did have the option. I would hold my opinion. What seems to be most suspect is that the parking brake was not used, failed, or was inoperable. Clearly the car was not properly chocked ... surprisingly few are.
Careless? If David is saying that the handling of high end concours cars is rarely careless, that is true. "Fussy" is a better description. It's very common for high end cars to be handled not by the owner but rather by a crew that insures that the car will be properly prepared and protected.
By the way, this happened at Hilton Head. This was not a mall show where spectators and their kids climb all over the cars ... or reach in and hit the starters.
I don't know at what point in the show this happened. Was it during set up in the morning or after an award presentation with the car returning to its parking spot. I can assure you that there are plenty of distractions when moving a car around on the concours field. Early in the morning at daybreak with the dew still on the ground and numerous concours staff directing and parking hundreds of cars in their exact spot ... or parading to receive an award through throngs of people. There is a certain level of distraction that may have played into this.
Point is that somebody screwed up due to an oversight, distraction, mechanical problem/misunderstanding. As in aviation, most accidents are attributed to "pilot error."
It will be interesting to see if more is reported.