But doesn't seeking diversity induce a bias in and of itself? By assuming people with a different skin colour or family name have some inherent difference we are in fact acting in a prejudicial manner.

The article does not state that diversity actually offers any benefits. It describes the benefits of being unbiased, and then equates that with diversity. Diversity is a very poor measure of bias (as shown by some recent little javascript web app demonstration); rather diversity is indicative of bias and it takes bias to create diversity.

Don't confuse the goat with the milk.