Bob is right. Apparently, polymer is not as absorbent as paper, so the ink dries on the surface and can be easily removed.
"Pre-printing folding errors" are actually not a new concept. When a sheet becomes folded or has creases running through it, the printing will be offset and there is usually a cutting error associated with the fold. Adding the words "pre-printing" to the description actually does not mean anything. I think it's just a buzzword to make the note sound special and attempt to fool you into thinking anything about the seller's description is correct. I don't believe the note is uncirculated either.
By astounding coincidence, I "found" one of these purported errors on a $5 note. Not only does it have a white gutter, but there are subtle design differences too.
{https://imagizer.imageshack.us/v2/1000x478q90/673/04dea4.jpg}
Image source:
http://imageshack.com/i/ip04dea4j