On 9 April, user u2u3 opened a forum thread about how to buy 200,000 to 400,000 bitcoins
"in the next few months" at $2 per coin. This was at a time when the going rate was less than a dollar per coin, and a price of $2 seemed unthinkable for the near-term.
After a brief discussion, u2u3's conclusion was that "Buying up slowly on MtGox is probably the way to go".
Maybe u2u3 got his $400,000 cleared, and has been "buying up slowly on MtGox". MtGox transaction volume shot up on 12 April and has been generally high since then.