OK, I finally I clicked on the link, here is what the boss said: ""For customers who had buy orders filled — we are honoring all executed orders and no trades will be reversed. For affected customers who had margin calls or stop loss orders executed - we are crediting you using company funds." So I guess nobody got hurt because of margin calls and stop losses, but a bunch of guys got lucky with buy orders filled at very low prices, and the whale sold out his position at a very unfavorable average. I am guessing the exchange will make money out of this, assuming ETH's price staying up...
Well, there is really no good way to cash out of a huge position, unless someone also uses options. Let's say the same whale would have thrown smaller chunks at the exchange, the price would have gone down just the same after all the order book doesn't become thicker suddenly. Now if he does that slower, people have time to panic and other sellers jump in cascading the sell orders. If I had so many coins I would just play both sides of the market and let it yo-yo like crazy. Push the price down, then switch to the buy side, rinse and repeat....
For Etherium I don't know but for Bitcoin you have Auctions where you can dump large numbers (if you spread over a few days): https://gemini.com/auction-data/
Why is ETH heading back up to its all-time high? Has anyone read CNBC today to find out? Those issues Etherium had a few days ago must be resolved now. New CNBC headline "Investors confident Ethereum will resolve its issues, surges towards all-time high".