Well it was confiscated and in a way they were holding them thus suddenly if they will sell all of them then the price will fall even lower and am afraid before bitcoins are getting recovered from this south Korea will make some move.
It's kind of unfair, Everything is gonna give it a massive blow.
Typically the US government has auctioned off Bitcoins to the highest bidder- they don't go through exchanges. They're also usually sold above market price, since it's difficult to purchase such a large amount of BTC without driving the price up. OTC exchanges like this generally don't have a negative effect on price.