I don't think he's saying that there's anything fundamentally not neutral about IRC as a technical product. I think he's pointing out that the fact that it is gender neutral from a technical point of view does not mean that the experience is gender neutral in practice, because, as you've pointed out, people bring their own biases to the medium.
I believe his point is he realized that technology alone does not obviate sociological issues, after being confronted with his own bias in an unanticipated way.