I've read it as a time reference. He got trialed after the conference.
Edit: In this thread:
> I wonder how the arrest went down, why he took a plea, what the details of his presentation were
>What if he did the exact same presentation in youtube, and in NK they saw that presentation?
> The US sentenced a crypto researcher to five years in prison after he presented at a blockchain conference in North Korea.
> Prosecutors say Virgil Griffith, 39, undermined US sanctions imposed on North Korea.
> "The most important feature of blockchains is that they are open" Griffith said in his presentation, according to prosecutors.
You can draw your own conclusions as to why they went with the title they did.