With this diverse pool of candidates in place, they would ensure that the entire selection process focuses on whether a candidate can do a job regardless of their race, gender, religion, sexual orientation, and more.
It says "gender". I read that as using it in the way of "gender" being a polite way of saying "sex" and until recently no-one (or hardly anyone) would have thought twice about it.
I doubt very much the Army Cadets think they can refuse applications from one sex just because they are of that sex.