I think what they mean is — a world where there weren’t labels, no preconceived notions of gender. ‘Boys’ weren’t separated from ‘girls’. Having a penis would not lead you to be pushed into masculine activities and roles, and a vagina wouldn’t lead to femininity. In this world, would trans be a thing? Because, as a result, cis wouldn’t either. So in this incredibly (and sadly) idealistic world, there wouldn’t be a need, or a want from some to be different to the body they were born into, as it would inevitably match their interior self. Dysphoria wouldn’t be a thing.