I didn't respond to that comment because the argument is fallacious. Just because someone has previously acted without prejudice does not mean that they will always act without prejudice in the future. It is the "I'm not Racist, I have many black friends!" argument in disguise. Especially when it comes to non-personal entities there is no firm expectation of consistent behavior.

I'm not privy to the details of this story and there are always many possible explanations for any given set of observations. I can therefore not know for sure that the explanation is sexism, but it does fit the bill. Those who discard that as even a possibility are biased.