55k Bitcoin in a short position ? Holy mother.. 
55k contracts. IE $5,5000,000 which is 5.5k BTC and he's probably using 10x leverage so 5.5k/10 = 550
550 bitcoin short
Nope ... look again ... 55k BTC
Agree, probably on a 10x. So 5.5k BTC on the line as margin ...