On the other end of your fantastic trade, someone sold you really cheap Ethereum. But the problem is if there is really another human trader involved (a fat finger trade).
I think the exchange has no problem releasing the ETH you bought cheap if only there is someone that has sold you that. I think this is the problem when exchanges fake trading volumes or trades. They just sold you air and no ETH to give to you which is rightfully yours.
We can assume a lot. Even if the Okex was engaged in own machinations - these are their problems.
There are guesses that in this situation hacked the trading robot Okeech. Therefore, they offered a bribe, because they were own money and they could offer them. At the same time, they certainly do not make any statements, because if they admit to being a hack, then big investors will begin to withdraw their money from accounts ...