Hang on there now... You just told us that he can SEE what gear he is in, but that he has no physical way of knowing.
That puts 100% of the blame on the driver. He knew the shifter was different when he purchased the vehicle, he chose the vehicle, he bought it. No one removed or altered the mechanism after this purchase. The display was present and accurately confirmed that he was not in park. He also chose not to use the parking brake.
How about placing the blame where it belongs -- 100% on the poor guy who got rolled by his own car. That's really a crappy way to go.
Caveat: All of the above is based on "facts" from this thread. If the gearbox did actually display that the vehicle was in park when it was not, then the manufacturer would be 50% responsible - with the user 50% responsible for not using the brake.