I suppose they refer to the fact the DPRK uses crypto-coins to evade sanctions. It's not that their whole economy is based on them and really it seems most likely a large amount of the coins they do own have been stolen from the west via hacks so their exposure to actual risk should the whole thing go down in flames is likely to be lower and less impactful than if you as an individual invested in it and the whole thing went down in flames.

Fact is they don't do a ton of foreign trade so the actual amount of crypto-coins used compared to both total size of foreign trade with friendly countries like China and Russia as well as the total size of their economy which isn't foreign-trade oriented is pretty small so again it's not a big risk for them to use them for sanctions evasion whereas the exposure to an individual putting half their savings in crypto is a lot, lot worse.

I'm not particularly an economic expert so take my words with a grain of salt but I don't see crypto as particularly useful as an investment vehicle, it's basically a situation where you either got in on the ground floor and got rich off a fluke OR you're using them to do illegal things like buy narcotics or send funds to sanctioned or designated groups (though with the latter in particular the US can track an trace a lot of the coins back to people eventually so I really wouldn't risk it). Beyond that I don't think they necessarily have a lot of value. Most of the big investors got in fairly early so if most of the larger coins were to say lose 30% of their value they wouldn't be badly hurt whereas you if you bought now and placed your savings in them would be.