Hello, the pin showed in the image is the ground. Though the one with the benl link is also with a ground. You can see it in the picture its a piece of metal shown in the inner diameter of the female plug. You should be aware that if your male plug is not provided with this connector, your either can’t connect it to this socket or you will not have a ground.

He may not, maybe he’s talking about the sound when the car isn’t fast enough to alert people on the street, just to let know that something is coming. It shut at a certain speed I think