[xzins]

My memory says I’ve seen it on forms in the past. They didn’t like the word “sex” which was a bit racy.

[USFRIENDINVICTORIA]

Yes, “gender” and “sex” are often conflated — or (worse) “gender” used, where the correct word is “sex”. Probably, in large part, because of the reason you cite — too racy. However, it is also often deliberate — if words lose their meaning, it becomes impossible to have rational discussions of the issues. It's a “sex-reveal” party — not a “gender-reveal” party. When change-room, and bath-room policies are being discussed — sex matters a lot more than “gender”. The reasons should be obvious — but, obviously, they aren't, for certain people.