That is a huge amount that something you trust web wallet and you know that you didn't own the private key of your wallet. Sounds strange for me, how this comes up like this.
I checked that transaction of scammed address, it seems like 336 bitcoin has been divided into small amounts within different addresses, the last 85 amount of Bitcoin landed on this transaction address. It seems like the hacker didn't cashout yet Bitcoin into fiat.
Most likely the hackers are trying to hold it for now and staying cool for now. They'll eventually cash it out to fiat.
I've never heard this exchange before to be honest. Maybe they are trying to exit scam by making this fiasco? because any developers knowledgeable enough on cryptocurrency or Bitcoin itself knows that web wallet is not a safe way to store Bitcoin.