Its the difference between the purchase price and the settlement date. I've got no idea what really happened but can speculate that what happened was that an order to purchases 1.625M shares goes in, (that will cost $1B), the trades are recorded people who've sold get notified they sold @ $xx etc. Now the trader was hoping the price goes up by a few $, then sells again. Now if everything "works as planned" when the trades are settled at the end of the day the people who bought put their money in the people who sold get their money out and the left over is in the bank.
But if you buy the shares in the morning and the price goes down, if you want to 'hold' and wait, you need $1B to cover the purchase of the stock, but if you want to 'cut your losses' you just sell the stock again for what ever you can get before the markets close.
I'm guessing this was what happened, and at the end of the day the difference was $5.3M which the company had to come up with to balance their accounts. That left them with not enough money for day to day operations, poof they are dead.