Pirate dropped about 10k BTC last month and the price dropped from $9 to $8. He dropped 100k BTC over the weekend. It was bound to fall. He can only drop it that much 4 more times.
Plus, I think you are underestimating the possibility of there being
much deeper pockets that Pirate which kind of enjoy shaking the Bitcoin tree to see if any bitcoins fall out. And from another thread:
I have already started helping some people formulate a USD/gold to Bitcoin carry-trade.