You also have no idea that this wasn't just data mining without an out of sample test. I've found lots of spectacular strategies using Quantopian that then fail spectacularly on an out of sample or forward test.
I think the author had a pretty robust backtest with minimal parameters which would limit data mining along with a 42 year period lookback.
As far as buying the dips on indices, good idea but far from a strategy. A strategy, to me at least, needs a concrete reason to enter and a quantified exit.
I appreciate all the feedback, it seemed like a reasonable strategy, that won't go to the moon and won't blow up either.