Let's say i sell candy with the profile of Kim Jong-un online, based on your answer that would justify North Korea to hunt me down in other countries and take me back under their jurisdiction? Gladly that's not how it works.
2) Selling candy with profile of the Dearest Leader is not recognized as a crime in most countries by treaties they've signed. Copyright crime is in many countries, hence it's extradition-possible.
2b) Copyright crime isn't a capital offense, so "but he might be executed" is not a bar to extradition here. Most countries would view lese majeste in Best Korea as a likely capital offense and wouldn't extradite on that basis alone.
3) Dude wasn't a citizen of the country where he was caught. Non-citizens have substantially inferior rights in most countries, particularly in this kind of matter.
4) Ukraine isn't in EU.
5) Because it's the ultimate factor here, it bears repeating: the US Government has essentially unlimited power globally. It is restricted primarily by its own policies, and by secondarily realpolitik concerns. Only in extremely few places is its power actually checked by another actor (Russia, China, and in some contexts, the EU, and in other contexts, Iran and North Korea).