At least a quarter million South Koreans lost money. If he is returned to South Korea, he’s going to prison regardless of whether or not he deserves to. That’s how the world works, IMO.
That being said it seems like there is more to his story than buggy code.
Fraud requires intent in most jurisdictions. This looks more like gross negligence (and possibly embezzlement). In addition to, likely, a host of money transmission law infractions.
Take Martin Shkreli, for instance. I don't doubt that he was probably guilty of what he was charged with (unrelated to his price hikes of drugs), but I doubt he would have been charged if not for his infamy otherwise. I suspect what he was charged with would also encompass many other business people in the US who are less infamous.