Neutral and Drive are very close on the gear stick. Maybe he wanted to check the mail, accidentally put the car in Neutral, went to the mailbox to be smashed in the back by the car, hit his face on the mailbox, lost consciousness and sustained fatal internal injuries because of the car hit My theory
His death confuses me though. His car apparently rolled down a hilly driveway and pinned him against a gate and killed him. The way the descriptions from articles reports it makes it seem confusingly bizarre.