It seems most likely that another algorithm was looking at the full book and reacted to his spoofing order with it's own orders (that were actually executed) an

It seems most likely that another algorithm was looking at the full book and reacted to his spoofing order with it's own orders (that were actually executed) and which accelerated the price downward. This would have tripped algos looking at momentum and other stop loss orders in rapid succession. This is why it's dangerous to have algos run on the full book, especially without some logic to remove outliers.