I believe the parent comment (it is flagged now so I can't be sure) used the term anti-feminist because the author has previously described herself as an anti-feminist.

To the question, it is anti-feminist by its acceptance of the unequal social status of men and women today. Both the feminist and the anti-feminist agree that there is social inequality between men and women, but to the feminist the best action is to create social equality while to the anti-feminist the best action is for men and women to act appropriately to their differing circumstances. The thought that "a woman ought to say no" to unwanted experiences is focused on adjusting the behavior of the woman to her current unequal circumstances and is thus anti-feminist. A feminist would agree that women should say no to unwanted experiences, but will also say that women should not be exposed to so many unwanted experiences to begin with.

Honestly, I think it's because there's this feminist idea that a woman should bear no responsibility for anything labeled bad that happens to her, especially if it involves anything sexual.

Like most things, that idea began as one legitimately applied to certain, limited circumstances; but that complexity was forgotten in its popularization. Now we're left with an over-simplified (and wrong) remnant that's still treated as gospel.

It's difficult. It essentially comes down to whether sex should be opt-in or opt-out. I think it should be opt-in, either verbally or non-verbally.

This case in particular is difficult because "Grace", according to her account, was sending mixed non-verbal signals.