And people who knew what they were actually talking about were pointing out that it's unlikely anyone would have voluntarily left Jane Street as early as he did. But they were largely ignored.
Leaving Jane Street to become a Billionaire seems like a weird criticism
I read he was there for over 4 years, is that abnormally short? Seems like a pretty normal period of time to me.
Seems like a weird critique to me. Some people join out of college and realize that, for a variety of reasons, that sector isn't for them (yes, even at Jane Street). Maybe they get overly enamored by an internship; maybe they don't want to live in NYC. My impression is they are pretty 'open door' about rehiring if you leave on good terms or decline an offer anyway.
It seems likely that the Kimchi arbitrage (arbitraging between exchanges in Korea an the rest of the world) was indeed massively profitable. He took a wrong turn later.
When I saw that he was using that as the claimed origin of his wealth I wrote him off as an almost certain fraud.
Why? He must have had some money of his own and some rich friends to set it up. So he had the means. Also, the difference was there and it was persistent so he had the opportunity as well.
There was very little volume available on those pricing discrepancies, making thousands per day without erasing the arb would have been a challenge but perhaps not impossible. The public is expected to believe he made over $10 million dollars per day on average on that trade. It's not credible.