Gender has replaced sex as the favoured word in general usage. Partly, because it's seen as more inclusive, also usage trend. I see it in aquarium forums; people asking about their fish. You are assuming a lot about that animal that can't talk when you ask us to tell you its gender!

Gender didn't "replace" sex, they are still interchangeable. In a country where being transgender is illegal it's absolutely just letting your bigotry on full blast to make this point.