That can't be right, 10k is not unusual volume.
However, I was watching the bids getting hammered out of the bid book for days. Consistently. E.g., every time a btc buy order was placed, it was removed. The books were kept clean, and the hunt for margin calls was opened. Quite impressive really.
I got the feeling it was very deliberate. A large sell order might have been the trigger, but the situation was not natural.. I was a bit confused by how thin the ask side was, very inviting to keep your long position open, because there was little resistance.. I remember seeing 4500btc to 285 when I closed my position at 252: eary.
Anyway. Margin calls on a long position are just as scary as margin calls on a short position, apparently..