The Wikipedia article you link to also claims that the 1882 Oxford Etymological Dictionary of the English Language said that one meaning of gender was sex. Other dictionaries from well before 1955 also support this. In fact, the 1828 Webster's dictionary, available online, specifically says the meaning of sex came first, the meaning in grammar followed from that. The separation of sex and gender is recent, you're right about that and that's what I was saying too, but you're wrong that sex was the only term used before that.