1,000,000,000 Won = $875,853.23 = ~330
BTCthis is not even in the top 20 exchange hacks in the history of bitcoin

this is more like the amount that some whales lose if they have a bad trading day...
According to Coinmarketcap, Bithumb is at 4th place in terms of BTC trade volumes. But it may be a temporary spike due to the news of hacking. Also, in Bithumb, ETH and LTC volumes are much bigger than that of BTC. This news came at the worst possible time. There was speculation that South Korea was going to legalize Bitcoin.