Your example contradicts the claim. They say "assigned male at birth" rather than "male", because they believe you can be a female even if you were assigned male at birth.
This is one of the closest-to-perfectly-binary phenomena that exists in nature.
Frankensteinian surgical mutilation is not really "changing genitals".
[1] https://my.clevelandclinic.org/health/treatments/21526-gende...
Gametes are not "several bimodal spectra." They are a single binary. And they are what define male/female.
I'm not sure that's a contradiction so much as it's trying to weave through people's own synonymizing of the two terms where a distinction is being made. I hear your point though.