The North Koreans could have tested a small fission core with hydrogen boosting, a necessary development for a larger megaton class device. And said megaton device would be significantly smaller then a 1/2 megaton all fission weapon. Thus if they were testing a hydrogen boosted weapon they have made a significant step towards deploying a megaton class hydrogen bomb.
Now a lot of groups are poo-pooing this story, showing what to me is there racial bias. The major anti-nuclear groups have been ignoring or down playing the North Korean program for two decades. All to promote what Jimmy Carter did during the Clinton Administration. Well Hillary finally needs to say something about that event and what it has resulted in. Bill didn't want Carter to go to Korea and he certainly didn't want the agreement he brought back. Now we have had the 4th successful nuclear test by this country and the possibility it was a key test of an even more powerful weapon. At minimum, this was a very successful test of a fission device given its yield.