This, and studies like it, are used to impose diversity on groups that would otherwise not have it, whether by intentional exclusion or by unintentional "doesn't fit the organizational culture." It's not surprising to me that groups which are spontaneously diverse are productive, and I'm perfectly happy to go with the 'open minds accept diverse solutions and diverse people' argument. The question that interests me is whether you can impose social diversity on a group, force them to open their minds, and subsequently become more productive.
I can certainly see where putting a person of color, or a woman, in a group of racist, misogynist bigots would disrupt their happy groupthink and break up their productivity. Regardless of whether that productivity started out a little lower than an equivalent group of non bigots.