If people are made aware that you're 10:1 in any direction, and they know your base price and level of exposure, it's simple maths to take advantage given that they have the resources to go against your position enough to liquidate you. In this case that appears to be what happened.
Definition of 'Stop Hunting'
A strategy that attempts to force some market participants out of their positions by driving the price of an asset to a level where many individuals have chosen to set their stop-loss orders. The triggering of many stop losses generally leads to high volatility and can present a unique opportunity for investors who seek to trade in this environment.
Who were interested in this liquidation? nobody would buy 20 000BTC just for fun, and nobody could get profit from this trade except..... right.. bitcoinica.