Twitter user @ismailtarim977 explained the recent controversy around the huge closure of Bitfinex Shorts.
When you short you are basically borrowing bitcoin to sell, hoping you can buy back later, pay off the loaned bitcoin and pocket the difference. This is called a naked short. If the market moves far enough against you, the exchange will auto close your position (buy back the bitcoin you borrowed using your collateral) this is a called a short squeeze and causes the price to shoot up because the exchange just does a market buy. Every one assumed this was going to happen, buy this guy had already had 20k bitcoin in his account so he closed the position himself.
A very smart whale, if this is what was triggering the short closing.