I thought it was a useful distinction that gender and sex referred to different things. To say nothing of the law or the article, I think it is good not to conflate them. If the field is to be on the ID, and maybe it shouldn’t, then it should be marked as intended; sex for sex or gender for gender.

Maybe there are reasons sex is beneficial, with respect to emergency services and immediate knowledge of biology, but maybe it would be better just not to have the field.