He's saying "gender" exists independently of "gender roles." He's got it wrong. Sex exists independently of roles. Outside the context of grammar, "gender" is nothing but roles: it's how a society expects people of different sexes to act.
To the extent that "sex roles" exist, they are strictly reproductive. Men inseminate. Women are impregnated, they gestate, they deliver babies, and they lactate. Beyond that, for just about any verb that you wanted to tack onto the subject "Men" or "Women" ... that is, "gender roles" ... you can find an exception in living or historical anthropology.
You have a valid point. He is clearly using gender to mean sex. 2 years ago that was a legitimate distinction. The meaning of gender has shifted in just the way he describes as the very purpose of progressive deconstruction. A word that meant something very specific just a few years ago means something completely opposite today. That is the very case he is making in this article.