You miss the point. The entire purpose of stamping "classified" on documents to to remove doubt as to whether or not that information is restricted. And, even though a non-stamped document may still contain classified knowledge, if you provide that knowledge to someone without knowing it's classified nature, you are not guilty of a crime. You've done nothing wrong.
In this case, the government didn't ban a specific bit of information. They decided after the fact that some very general knowledge about blockchains might assist North Korea in evading sanctions. If you post to a message board that you believe sanctions on Russia won't work, because Russia will simply buy through China, have you just aided Russia in evading those sanctions, by stating the obvious?
In this case, it's even more absurd. Nothing this man said in his brief speech was more than common knowledge. I've seen more detailed information on the benefits of blockchains posted to this very message board. Under the theory of this indictment, North Korea can freely access that information from this board --- but if you print a hard copy of this page and walk into North Korea with it, you're suddenly guilty of a heinous felony. It's nonsensical, and indefensible.