Willful ignorance in service of their agenda. The facts don't matter, TERFs will bend any situation to make it conform to their anti-trans beliefs because they're THAT deep into their hatred.

I've also seen them claim that women are "biologically disadvantaged" at skateboarding, chess, and (sit down for it) beauty contests. One really gets the impression that TERFs just think cis women are pathetic and trans women are the pinnacles of humanity or something.