Every time someone discovers a new way to make money with such a high return it's almost always because they are the first to enter the market providing an actual good or service or they just discovered a significant technological advancement giving them a huge edge over the rest of the market, neither state of the market can last for a long period of time because competition soon follows and diminishes your slice of the market pie.
Um, yeah, it's called bitcoin, have you heard of it?
And he has stated that he doesn't want to reveal exactly what he's doing because then other people will do it, driving down his profit. Which also fits with your theory as quoted above.