It appears to be. (Obviously complete nonsense.)
But let's just give them the benefit of the doubt for a second and assume it is true. That we have literally no way of telling whether someone is male or female unless they strip butt naked.
Trans people know what kind of genitals they were born with.
If we say that people born with male genitals should not use female only spaces, and in particular if we provide third spaces for people who feel unable to use spaces for their own biological sex, shouldn't that be enough?
If trans people are as lovely and harmless and trustworthy as trans activists claim they are, surely they will do the right thing and respect the rule?
And if not, well that kind of proves our point, doesn't it?