If this story is true, it sounds like an explosive device was included in the "low-tech" North Korean junk.
Very interesting. Maybe South Korean intelligence planted it; maybe the CIA is better than we give it credit for. The implication alone is useful as it may cause the Iranians to suspect the North Korean source as saboteurs.
You always have this problem of enriched uranium separating water into oxygen and hydrogen ~ when it heats up. That's what blows up those atomic power plants ~ or any place else that's not properly ventilated.
So, an underground facility full of centrifuges blows up ~ certainly not news.