I've seen people claim that here too. Not exactly true, but gender did probably become a synonym for sex because of prudes not wanting to write sex. Once people learned it was an acceptable "alternative", usage exploded. Of course it actually refers to grammar, and the certain properties of objects that are denoted as masculine or feminine in languages that have that feature. It serves little purpose in English.

And yes I've stopped using "gender" for the most part thanks to these freaks. For work I build databases to collect customer personal information for company records and surveys, and will often have someone come to me with a request for the standard demographics fields, "age, race, gender...", and I always deliver them a database or report with fields "age, race, sex". Haven't had any pushback yet.