"The report’s authors, ...  found there was no significant performance difference between companies whose CEOs were women or men."

So this is a problem if you think the study reveals that venture capitalists are biased against women headed companies. What it reveals is that venture capitalists look only at the bottom line, and are just as good at evaluating proposals from male CEO's as female CEO's. 

There may be reasons why women headed companies do not fare as well as male headed companies under the same circumstances, that are not the female CEO's fault. This could be bias in other markets, among customers, etc. In other words, the bias could be systemic. But to prove bias among venture capitalists in particular you would have to show that the female headed companies they fund do better than male headed companies they fund. This would mean they are as likely to fund a mediocre male proposal as a promising female one. That would be bias.