First of all, we don't know for sure whether this story is true or not. Even if it is true, how much impact $400 million sale is going to have, especially when the daily trade volume is around $6.5 billion? If the sale was spread out over a number of days (which looks very likely), then I would say that it would be having a very insignificant impact on the prices.
I can agree with you,if Kobayashi sell 400$ million worth of
BTC in few months time this could not have been the only reason why price is started to move down.Based on some daily volumes it is not even 10% of some usual day on the markets.It is clear that the price was unrealistic and the correction was inevitable.I bet some whales have info about MtGox and they just got scared Kobayashi will crush price down,so the sale began.
Regarding the remaining amount of
BTC worth around 1.9$ billion,I do not believe it will be available for sale soon.I think the current price does not satisfy Kobayashi and the ones he represents.I'm not sure is there a deadline in which remaining
BTC must be sold,but if that is not the case they will probably wait new ATH.