From what I understood from the post you shared, Kevin did not have access to all those
BTC259684.77 he was able to withdraw only 643 btc, Because, of the limits that MT Gox had at that time, In my thought, Kevin made mistake for talking to the CEO of the MT Gox and telling him about the situation and how he able to buy that much BTC at that low rates. I mean, this is all so crazy at first hand, I did not realize, things were that faulty back then.
Well, overall, the story is really fascinating and really a good one too, I hope Kevin will have access to those 643 BTC that he was able to withdraw from it.
You are correct Kevin to take this approach. I believe Mt Gox tried to fuck everyone, especially you. I believe they may have stolen bitcoins from accounts, then tried to sell them to buy them back up, thus laundering them into their own hands.
That's just my opinion, based on everything I have read and heard so far.
This might be a possible reason behind that sell order, well, overall, this is so messed up.