These are assets, electronically managed like every other bank account, frozen administratively based on US policy toward rogue states. The money might well have come in part from sale of counterfeit money (or drugs, weapons, etc.) but there are no bogus bills sitting in a bank with NK's name on them just waiting to be spent.
They were frozen because they were the fruits of illicit activities.
What I want to know is what this administration thinks it is going to do when, not if, Kim thumbs his nose at the agreement once the funds are released.
I hope noone seriously believes that NK will really shutdown
the reactor in question (Yongbyon).