It's hard to know if the returns are statistically significant given annual returns, but I'm sure he's providing more granular statistics to investors. Kinda annoying how the articles hypes this by distinguishing it from statistical models since he is obviously running some sort of statistical model as well.

In general, people have a poor understanding of how to evaluate an investment manager. It's not enough to just look at absolute returns and compare them to the S&P, you need to correct for market exposure (the beta). Even then, it is not that straightforward: this is one of the best overviews I've seen (the author of the blog, Robert Frey, was a former managing director at Renaissance Technologies, the most successful hedge fund of all time)

http://keplerianfinance.com/2013/07/alpha-and-evaluating-inv...

To make the "correcting for exposure" aspect concrete, suppose you have the opportunity to invest in a poker player that generates a 10% return on capital per year. It wouldn't really make sense to compare this return to the S&P 500 returns, because the beta is very close to 0.