Wordsmiths/parsers like John F'n Kerry are rarely, if ever, held accountable for their words. This one will be no different. While what he said is obviously wrong, I'm not convinced that really, truthfully, and honestly, that he doesn't know the Norks have nukes.
It's just another politician who misspeaks. Happens all the time.

It happens all the time because these kinda guys don't actually do anything -- they just talk. And since talk consists of words, it stands to reason that once in awhile (okay, okay, with Slow Joe it happens pretty much on a daily basis), they're going to say something that's factually incorrect.
By all means, let's squeeze this idiot like a rotten fish and let's see what kind of stink comes out. But it's still gonna stink and it's still gonna be rotten.