Re: Work with facts
Go check out dictionaries from even the early nineteenth century and you'll see that the term "gender" meant "type" first and foremost and it was well-known that it was being used as a synonym for "sex" by application of the original definition to observed "types" of animal.
Early twentieth, that secondary use of "gender" was regarded as obsolete or localised.
It picked up steam again during the twentieth to mean what it means now in relation to typing of humans, which is distinct from the original conflation by virtue of the fact that a) we know a shedload more about biology now and b) since the near-universal accessibility of dictionaries and education, any given person that you come across is more likely than before to be a semantic pedant.