It doesn't distinguish sex characteristics. It denotes identity.
The issue is that evie doesn't seem to be up-to-date with gender identity - evie is frequently talking about transsexuals, and seems to be using "trans" to mean "transsexual", or "has had some sort of surgery to attempt to imitate the opposite sex". Which then makes "cis" "has not had some sort of surgery to attempt to imitate the opposite sex".
Given those definitions, "cis" is meaningful. It's true that most of us have "not had some sort of surgery to imitate the opposite sex".
But that's NOT the definition of "trans" in common use, and hence it's not the definition of "cis".
"Trans" means "has a gender identity different from their sex/assigned-sex-at-birth/assigned-gender-at-birth/whatever-you call it". "Cis" means "has a matching gender identity".
That is the offensive nonsense - the claim about our non-existent gender identities.