As far as I can tell the best evidence they have for this is a widely circulated video (from before FemFreq) in which she says she's "not a fan of videogames".

And some Feminist Frequency tweets repeating what McIntosh posted before: 1, 2, I think there are more but I cannot find them now. (Memetic hazard: here is the "argument" in a form of a youtube video.)

By the way Feminist Frequency is a project account, not Sarkeesian's private account (although it uses her photo), so it wouldn't be a damning evidence even if McIntosh would really sometimes use it. Also, when two people cooperate and have similar opinions, it would not be so unlikely to use the same words. = this is just a weak evidence