Sex is the biology; Gender is the identity. Discrimations are based on gender, not sex. Women are told to wear pink dresses because of how our society see women (female gender), not because they have a vagina (female sex).
Based on what the dictionary says? The idea that gender and sex mean two different things isn't contentious amongst the people who study the phenomenon academically.
Do you feel the same way about all social sciences? Does "materialism" only mean valuing material things to you or do you respect the Philosophical definition? Honestly it's a lot of handwaving to excuse ignorance (what not knowing the difference between the two terms is)
Every generation of soft social "scientists" (I use scare quotes because they don't usually use the scientific method. When I say "soft" social scientists I mean e.g. Gender studies people as opposed to demographers.) tends to disagree with the previous generation on huge fundamental tenets for mostly arbitrary reasons. It is wise to take any dictionary-defying claims from these fields with a large grain of salt, because there's a substantial chance that such a claim is made for social or political (but not scientific) reasons.
The general statement "they mean something different" is a pronouncement on language as a broad concept. The OED and Merriam Webster are about as authoritative an answer as you can get on that in English, which for the sake of HN, will have to do for now. That's not to say one day the differences won't evolve (linguistically) into fairly concrete and well-understood distinctions across all languages, but we're definitely not there yet.
Regardless, these factors are in a 1-to-1 relationship for around 99% of schoolchildren in the third grade "aged 9 years old on average" including, presumably, every single child studied in this study. Discussion of the specific differences, or of the other cases, might have substantial merit... but seem less than productive on this particular occasion as the topic is at best only tangentially related.
What evidence do you have that identity doesn't originate in biology?
I'm well-aware of the existence of transpeople, but I'm not ready to conclude that gender dysphoria doesn't originate in biology. There's more to a person's biology than their genitalia.
We only need it because we live in groups. If we were all by ourselves we would not need this language (and much other language). Much of language is for signaling.
