Its not clear from the article which factor the 50% figure applies. I doubt its the overall odds ratio, but rather the likelihood given some priors. For example, given a prior that 90% of startups fail, what is the likelihood that this particular startup will succeed? If the prior is already factored in, then the model predicts no better than a coin flip.
The point made in the article is that investing at the odds of a coin flip would be better than investing with incorrect risk assumptions (ie. buying into "particularly bad ideas").
Assume startups fail 90% of the time. 50% of the time your coin comes up tails, and you claim the startup will fail. 50% of the time your coin comes up heads and you claim the startup will succeed.
You guess correctly 0.5 (the chance your coin comes up tails) * 0.9 (the chance the startup fails) + 0.5 (heads) * 0.1 (success) = 0.5 of the time.
The point made in the article is that investing at the odds of a coin flip would be better than investing with incorrect risk assumptions (ie. buying into "particularly bad ideas").