Nothing would surprise me either these days. However, this just doesn't quite seem right. The purpose of a nuclear "test" is to scare the crap out of the world. Therefore, these "tests" like those in India and Pakistan are usually publicly announced very quickly and likely exaggerated for maximun publicity. Really, I mean, there is no point in being the nastiest barbarian in the neighborhood if no one knows it!
We will see. Most likely it was a conventional accident of some sort. Which again demonstates the N.Korean inability to run an obsolete Stalinist state. They can't even feed themselves while South Koreas big problem is selling enough TVs and cars to the impoverishing West. FWIW, my monitor is an old cheap Samsung which still works as well as when I bought it 3 years ago.