I wondered about that too.
I think most cars these days only engage the backup lights when the car is in reverse.
In years past, there was a switch.
If he was in R, he must have had the E brake on.
It would have had to be an automatic transmission, otherwise the engine would have died with it in reverse gear and the emergency brake or parking brake engaged.
Strangely, during my 25 years working for a city fire department I went to a lot of people who were drunk and/or on drugs sleeping in running cars. Often the car was in the road, surprisingly often in the middle of an intersection in drive with just their heavy drunk foot on the brake keeping the vehicle from moving. And a of course we also went to many cars that were still running at the side of the road with the person still asleep after a low speed collision with a post, poll or other solid object. This actually happens just as often as a drunk falling asleep at highway speeds and running off the road. Only that is traumatic enough that they are usually awake or dead.
One time we went to a guy who fell asleep and had run over one a planter in the middle of one of those new round-a-bouts. It split his car into two pieces which were still connected at the floor, but it looked very strange. Unfortunately, his feet were in the front half and the rest of him was in the back half. He was sleeping or unconscious when we got there. But when we decided we had to get him out in a hurry and I started pulling on him he perked right up. His feet were catching up under the dash and both his ankles were broken.
One of my crew yelled, “don’t pull on him anymore or I think you will rip his feet off. So we had to spend a few more minutes getting his feet unhooked from the mess he had made out of the front of his car. Along with the smell of booze we kept smelling this strong solvent odor.
In the trunk he had a bunch of chemicals from a portable drug lab. Some of which were broken and creating a fire and health hazard for everyone on scene. It is possible that the chemicals were partially responsible for his inability to stay awake. So life lesson #246, if you are drunk and waiting to move your drug lab in the middle of the night... make sure you take a nap before hand. And also make sure that none of your solvent containers are air tight. If you can’t do that at least choose a route that has no round-a-bouts that might get in the way while you are snoozing in your car.