Pump and dump or was it a well calculated move?

Yesterday, we were trading in a tight bull flag at around 242. I made a call and went long at this area expecting a breakout higher. I did not capitalize it, got shaken out before the rise. However, I've noticed something very interesting. There was a huge margin call on the short side valued at 11825 contracts. Take a look at the numbers below. How big is this size? the second largest account holder on OKcoin.