You got me curious so I had to look at it between lunch and weed whacking.
If it’s the pin by the pulley on the motor, I don’t know why it’s there but it isn’t to be a keeper unless mine is messed up. Mine only has 55 hours on it. A stick got on top of the deck at about 6 hours, derailed and shredded the belt, so this is the second belt and admittedly I put it on. 49 hours either way no problems thus far. Yes, it’s on the inside of the belt. It has nothing to do with the belt.
This is the view looking straight up from the floor toward the motor output shaft/clutch/drive pulley. The pin is on the lower part of the picture just above the belt and almost touching the pulley. As you can see, if the belt is routed to the inside of that pin, the pin would scrub the hell out of the belt. To make it worse, the pin is flattened on the end. If routed inside the pin, the belt would be scrubbing on a corner of the pin. I sort of doubt the belt would last more than a few minutes routed behind the pin.