Seems like it was a tip from inside the company, probably someone who understood that it's better to come clean and avoid a prison sentence if all goes south..
One other thing is the sum involved, 8 million $, really low for a top exchange, what's that, not even 1000BTC ?
Don't know really about the SK government in internal affairs but in the virus crisis they acted faster and better than almost anyone on this planet, maybe when it comes to crypto they are taking their sweet time but overall I'm considering them one of the most efficient out there. Besides, that's not even the government business it's directly anti fraud police work.
Let's assume there books don't match, poeple have deposited 1000BTC and there are only 100BTC in the wallets.
Insiders would take advantage of the news and some clients will get all the money out and some will be left with zero, lawsuits will fly like fireworks on 4th of July against the police.