"a micro size nuke" As long as it wasn't a fizzle, the smaller the blast, the more sophisticated the engineering. Conventional wisdom was they could only build a heavy, inefficient bomb and therefore could not deliver it on the tip of their missiles. The smaller and more sophisticated the device, the more the delivery options open up. We rightly will not hear most of this discussed but I wouldn't be at all surprised that the NK has a lot of pointy-headed people saying ruh-roh.
It really depends what sort of help they've gotten. Many naively assume that the surface appearance of an isolated rogue state completely precludes outside assistance. Motivation? Simple. There are a handful of states with competent nuclear capabilities who have openly expressed, both before and after 9/11, that they very much would like to reduce /remove so called "American hegemony" from Asia and the Western Pacific.