He's talking about the trans.
For those that don't know, the A1R trucks have an odd sort of "park" feature in that model Alison. My truck sits on an inclined driveway (typically backed in). With the ignition on or the truck running, I can put it in neutral and release the brakes and the truck will just sit there on an incline as if in "park". I do NOT count on this feature to secure the truck, but I can release the air brakes and the truck will not roll as long as it's running (or the ignition is on).
I damned near killed myself one time as a result of this "feature". I was moving the truck over to make room in the driveway (I was parked facing down hill). I backed it up hill and set the brakes. I got out to check and it wasn't over far enough, so I moved it again and set the brakes. It required several attempts before it was in the right spot. Satisficed with where it sat, I reached up from the ground and shut the ignition off. Yeah, well it turned out that I had inadvertently not set the parking brake that last time. As soon as I flipped the ignition off, the truck started rolling down hill (with me standing in front of the front tire). Fortunately, I was able to grab the steering wheel and yank myself up and into the cab. I stopped the truck, but not before it had rolled out 20 feet into the street.
So yes, the A1R trucks have a sort of "park" feature in the transmission. And it disengages when the ignition power is shut off or the truck is put into gear. But it will actually hold the truck in place on an incline.