(Feel like adding Guardian in the title is click bait now!)
I'm still half asleep and it warrants a more thorough read but I feel the overwhelming results of the study were that it's the stereotyping of the adults that's at test here.
I think the guardian is attempting to make too many links to gender dysphoria and the title is rather misleading.
This could be misconstrued as early trans identities, but who / what really causes distress in a child who doesn't 'fit' with the gender stereotype linked to their sex? It's not from the child.
https://www.theguardian.com/science/2018/feb/16/child-gender-speech-age-five-research-university-minnesota?CMP=ShareiOSAppp_Other