Earlier quoted context omitted.
Correct he gave a talk at an academic conference on digital currency and Blockchain in which he described how a Bitcoin transaction works. Here's the article "He gave a Cryptocurrency talk in North Korea, the US arrested him" The slides are (or were?) available. None of the content of his talk was secret or beyond what is published on the Bitcoin Wikipedia page. https://www.nytimes.com/2019/12/02/nyregion/north-korea…
Going to North Korea and assisting them to launder money and bypass sanctions is illegal (aside from being utterly stupid and immoral), which is why he plead guilty and is now in prison.
Is that assistance? It is just a basic statement of fact. Is wikipedia guilty of providing assistance to NK? They provide far more in depth "assistance" to anyone wanting to perform a Bitcoin transaction.
Bringing this back to my original comment, you can see why the federal government would restrict the flow of fundamental technical knowledge by virtue of this extreme case. No source code or application was shared, no secrets or privileged information, merely encyclopedic facts were deemed illegal to share.
Also if you were facing the indefinite assange treatment I imagine you would seek a plea deal as well..