[youngian]

Why couldn't patio11 be speaking of gender? In fact, I think a study measuring gender would identify with even more accuracy, although data collection would be harder (you would need the authors to report how they identified). Anyways, the linked study uses the word "gender" - it's probably conflating the two, as often happens.

[aaronblohowiak]

... because he said that it is objectively verifiable

[youngian]

Which gender is. Your gender is how you identify, so unless you are lying to a researcher who asks you what gender you identify as, it's objectively verifiable.