Because the current rule of thumb is that ~9/10 startups fail. If you can reduce that to a 50/50 bet, you've made quite an improvement.
So maybe it's just bad or confusing wording in the article, the guy actually meant to say something else.
90% of the time the coin flip returns tails (aka fail).
10% of the time it returns heads (aka win).
For a given coin flip, their algorithm can predict the results 50% of the time. At this point I don't remember the calculations off the top of my head, but it involves a Binomial distribution.