It's fairly simple to look at the parts diagrams online. I picked out all 3 pins that were inside of the engine. The drain plug didn't have a pin.
Yeah I saw that too but the drain plug picture for the 1000 doesn't show a magnet either and I think it has a pin that sticks out. It doesn't stick out that far but it was a possibility.
Out of the three choices you gave I think the oil pump drive gear is the only one that would be that small. There's no way it could fall out so it either fell out during assembly, which would mean no oil pressure, or it is extra.