It's a "lost in translation" thing from Italian in the parts file. There's two seats listed. The second part is called two up in the part description. It's not referring to a pillion seat. The foam padding is thicker on the alternate seat. "Two up" the thickness is my guess. Here's a pic of one. I suppose a spotter could hop on the back if the next section was a bit of a distance, but it sure wouldn't be comfortable for either.