@titan20: Funds for bid orders are directly deducted from the current balance, as are the assets for ask orders. (no, it is not possible to go below zero balance)
If you trace back that account, you can find out that its funds come from one very big account (tens of millions), so it's most likely a NXT early adopter.
Thanks for the answer. Seeing the amount of transactions on the original account i think this might be an exchange.