Biden almost flew to Russia as a result of the exchange. Biden mistakenly boarded prisoner swap plane. Maybe he needed a quick piss. ; )

Grandfather went and boarded the plane after all the prisoners had already left, and finally realized. 

This was the plane from Russian that had just delivered the prisoners. That was to return back to Russia. Biden had just greeted the released prisoners from that plane, during the exchange.

Maybe he thought that he was part of the clean up crew.