The generic explanation is: The 'minority' can often have worse interview results and still get the job over a non-minority.
There was recently in the news a lawsuit against Harvard I believe, because there is some evidence that a White or Asian (minority in US but not in schools as a lot of them attend school) student can have better admissions testing scores and a "underrepresented" minority with lower scores gets admitted instead.
Wikipedia: In other countries, such as the UK,[7][8][9] affirmative action is rendered illegal because it does not treat all races equally.