Also of note that the complaint does not seem to have the actual presentation the guy did. The FBI must have been really nervous and interested in a certain line of questioning and topic. According to statement the audience left with a better understanding of blockchain and smart contracts then they had before. I don't think the guy held a presentation about "How to use Cryptocurrency-1 to launder money and evade sanctions". The 1 unit of Cryptocurrency-1 transfer from NK to SK could have been a hacker asking themselves: "Is this possible? Can I actually do this? What happens?". Well in this case you get the FBI-equivalent of blowing out the power in the neighborhood.
Of course, after the conference, some shady NK government employees came up to him and asked him more pointed questions (almost like an agent at the early defcons singling out Asian participants). It states they discussed "proof of work", not that the suspect was given a free (or paid) consultancy gig. I think they had nothing about the conference, so they had to wriggle all this out of him during an interview. FBI damn good at this. They got all the facts they needed to make this a convincing complaint. But reality is not straightforward.
I think you can think of plenty of other computer software nerds who got fucked by the law for doing what they do, and not murdering their wives.