I think you're interpreting the idea of luck incorrectly. Luck in this context is simply the phenomenon of being one of the start ups with high success. To say that success depends solely on luck means that the success of any startup is simply rand(). That doesn't mean all start ups are equally successful.
Giving selected startups money confounds two factors: the selection criteria and the extra funding. This means that any differences in the success rate can't simply be assigned to the selectors choosing wisely.