The whole story is complete bullshit.
Inside job, plain as day.
At any rate, this is the death of Counterparty.
~BCX~
Why would they put an exploit in their code, let it sit for months, then exploit it, then give it all back, making prices drop in meantime? hurting themselves, I dont see anything they gain by it?
If it was indeed an inside job, possibly he realized that the story was somewhat unbelievable and it was going to ruin the exchange's reputation, so he decided to return the BTC to save face and keep the exchange business.