So was this a failed test?

In the description below I noted that this was (estimated at) a half-kiloton detonation. Now it wasn't an earthquake because the depth of the event (see image in link above, or this image) was at the surface. There are no volcanoes in the area so this was, in all likelihood, a manmade detonation.

Initially I worried about the size of the device which must have been quite small. Think of the bombs we used on Japan. The resultant force of NK's device was something like 1/24 the size of those primitive devices, in terms of yield. So you can see with modern innovation, these could be used in conventional warheads, perhaps, or in a suitcase bomb. Frightening.

However, this could have been a device thought to be capable of typical yields, our first five successful detonations were in the range 15-25 kilotons I think. Our madness in the Cold War brought us up to around 15 megatons and the Russians to ~45 megatons I believe. (We humans are nuts). In those days we were breaking new ground, and the deterrence factor weighed into our calculations heavily. We wanted the Russians to feel our new power. Now that nuclear fission is a basic, easily replicated phenomenon, the deterrence factor has all but gone away. So maybe this was meant to be small for test purposes. But somewhere in the fission process, could the North Korean nuke have failed? This will certainly be used as the MO for our foreign policy geniuses; it allows them not to acknowledge NK as a nuclear state, which is the stated plan in the event that NK does go nuclear. And they may be right, at this point