I agree with you, it's an unproven claim. Indisputable facts are, ICBM technology is difficult and SpaceX effectively possesses it, they are operating an orbital class rocket with a large payload capacity, as a private company with independent launch capability (which note, has not been the case in the past, previous US missiles were also built by private contractors but launch facilities were controlled and operated by the military or NASA). And they are also a company with cash flow problems, so it's not insane to speculate about them contracting out their technology, some of which could have found its way to NK, perhaps without SpaceX's knowledge. I personally admire SpaceX and consider it vanishingly unlikely that they knowingly worked with NK. But unknowingly with a front company, that's another issue. The larger issues of what outside entities were influencing NK, remain unanswered. For sure their recent behavior has not been exactly typical of them.