The first part about why diversity is important has been covered ad nauseum so you can find those arguments and agree with them or not.
With that said, their survey includes companies across all industries, including those with a lot of customer face-to-face interactions (retail, banking, airlines, hospitality, healthcare). I am not aware of anyone narrowing down the research to tech/engineering field, so in absence of that the public just assumes that similar findings would apply to every industry, and diverse high-tech companies will outperform non-diverse ones.
If it's not the only factor, then there's a chance diverse candidates simply aren't being reached by the typical recruiter strategy. So companies take that hypothesis and incentivize recruiters to diversify their search. Only time will tell if that hypothesis is correct, and this is the only point in the system where race/gender are under consideration. It has no impact on those that apply to FB through a college career fair, or through facebook.com/careers.
As a minority I fully understand how race can affect one's perception on oneself, and how societal pressures can make one feel like they don't belong in a certain field. But in this light, shouldn't companies focus more on encouraging women and URM to enter in the field of engineering, and not at the point of hiring? CMV.