It's exactly what I said it was in my post. It is actually just hemipene shed. Ball Python females can be bred by more than one male during breeding season. More than one male can father a clutch with any given female. If male Ball Pythons actually produced sperm plugs then this would not be possible. Actual sperm plugs limit or prohibit another males sperm from fertilizing an egg. I think that the only snake that produces an actual sperm plug is the Garter snake.
It is this shed that the male produces that breeders believe to indicate that a male is ready to reproduce.