I have been wondering myself ..if these reports are true (yes a big if..but I can't dismiss what we actually have seen so far from them)...then the only explanation is China. That GDP and these technologies do not calculate lolKindly stop polluting this section with these drivels. North Korea can barely feed its own population and you're trying to compare it to Iran? Perhaps in the 80's North Korean has some technologies ahead of Iran but today, even Iranian universities are creating more advance technology than the N.Koreans.
North Korea, assuming most of its claims are even real are certainly importing most of these technologies from abroad. This notion that a country with a GDP of £28 billion has the resources to create Nuclear submarines, hypersonic system etc is something that even a semi-developed mind would find ludicrous.