This makes the most sense to me (from the article):
On the flip side, looking at the chart from Bitstamp, the dump occurred over a 10 to 12-minute period with the orders being continuously executing at consecutively lower levels than the market price.
Such a pattern reeks of manipulation but the tradeoff seems counterproductive unless they held high leverage short bets on another exchange, say BitMEX. Theoretically, the dump would cause massive liquidation of long positions thus ensuring profits for the trader.
Or a recent Crypto millionaire fat fingering it. Screams “accident” too, not thought-out action done on purpose.