How? Creating a diverse pool of candidates, and selecting the most meritorious individual from that pool, are two separate stages in the hiring pipeline.
Google's policy as stated in that quote is simply addressing the fact that entrenched network effects (known more popularly as "patriarchy" and "white supremacy") cause minorities – and, by extension, talented minorities – to be underrepresented in the hiring pool. It's entirely possible to enrich the hiring pool by focusing on minority outreach, yet still select from that pool the most meritorious candidate (who may or may not be a minority).
Yesterday there was a comment on another story to the effect of, "I [male] wouldn't introduce myself to a group of two or more women at a professional conference, because I'd be the odd one out." The ultimate loss of networking opportunities for women and minorities which stems from such behavior is what Google's policy (as stated) seeks to correct. Reach out to those women (or minorities) who were denied a professional connection due to their gender/race/etc., so that they are granted a chance to be judged on their merit, alongside others for whom the opportunity to be interviewed came as easily as getting a sunburn or growing a beard.
Granted, it sounds like what happened in the case in TFA was one of explicitly culling the pool to remove otherwise meritorious candidates based solely on their race, which is in conflict with the above policy statement.