As things stand, there are two major dimensions of misrepresentation on the committee: it is completely over-represented by women, and it over-represented (33% of the board vs 15% of the student body, and would be 40% if the candidate was brought on) by white people, and significantly underrepresented by Asian Americans (1 board member vs 33% of the student body).
Unless one makes the ridiculous argument that we "just shouldn't see race" despite it being a highly operative factor in our public lives, there is nothing wrong with the school board considering the problems of racial under-representation. They are seeking a qualified candidate who helps them address many dimensions of their demographic representation issues. There are likely many candidates who would be just as qualified but would better represent the community, like an Asian American man.
In fact, they didn't summarily say no to the candidate, just that they want to see a more diverse slate of candidates, and encouraged the individual in question to reapply. Of course, that part isn't mentioned by people who want to cast this as anti-white discrimination.