I think that was the MMs. You would have to be just plain freaking stupid ass DUMB to sell to the bid just there at 13. Clearly someone trying to manipulate for some reason.
Anyone with a brain could see that you could throw your order on the ask and would sell easily. But to drop your order down 4 points to 13 from 17 is just plain DUMB.
There is zero chance that wasn't the MMs doing what they need to do.