Gender can refer to either a
grammatical distinction
or to social and cultural distinctions -- identities, roles -- constructed around
sex.
"Gender bender" is a correct usage of the word "gender", but the phrases "gender gap"
and "gender discrimination," although common, would more accurately use the term sex, as the inherent distinctions are based directly on sex, as opposed to distinctions on the basis of "masculine" & "feminine" social constructions.
We can probably date these popular solecisms to U.S. Supreme Court
Justice Ruth Bader Ginsburg, who was a prominent women's rights lawyer in the 1970s
before she became a judge. At some point, she was persuaded by a colleague
to use the term "gender" (and "gender discrimination" and others) in place of the correct
term "sex", which Ginsburg thought might titillate or distract the all-male
panel of judges. She thereby set a precedent which
has subsequently confused the word's usage.