The government doesn't see Bitcoin as money. Instead it's just selling seized property like it always does.
I think the money in GP refers to the other side of the trade -- if you sell an asset on an exchange, you are going to then have money (received from the purchaser) that is yours on that exchange until you are able to extract it.
Ideally, that would be trivial, but that hasn't always been the case for BTC exchanges (Mt.Gox being a notable example for an extended period of time.)