Didn't you just answer your own question?

They're the only board members who aren't notable. After the ousting the board consisted of a prominent CEO in D'Angelo, a prominent researcher in Sutskever, and Toner and McCauley. It's a grouping of two randos, not two women.

You have three people, one of them is at least quite well known to the outside world, or at least his / her company is well known along with an ex Facebook CTO title.

You have two people left, we have no idea what he / she is, their work are not public outside of specific domain, and no Public / PR exposure to even anyone who follows tech closely.

Those two people we group them together. And they happened to be woman. ( At least we assumed their gender ). And we are now being called sexist? Seriously?