Yup, ‘boosted’ fission device at best.
Nah, a small dirty bomb at the most.
I think the biggest probability is a boosted device and the item in the photo the Norks released a couple days ago was put together using pictures found on the Internet just for scare purposes. There is a chance that they actually got all the proper components and the technology from someone else.
On the same line of thinking, did they get a guidance system that can actually put the device where they want it. even then they have shown the reliability of their missile airframes is not the best.