It's that much stranger because "partner" is an inclusive term meant to blanket everyone. "cisgender" literally means NOT transgender.
My wife is part of a two person committee whose sole role is to convert all of her professional organization's writing and copy into gender-inclusive language. cis-anything is gender-exclusive; the fact that it is used almost entirely by the transgender community to discuss things that aren't theirs does not promote inclusivity in the slightest.
Ain't nobody in Tuscaloosa, Alabama ever gonna think of themselves as "cisgendered." You can probably get them to accept Caitlin Jenner eventually, but they're always going to be "normal." Yeah, yeah. Transgender is "normal" too, I get it. But nobody is doing anybody any favors by requiring 65-year-olds to wrap their brains around a latin prefix so that nobody has the opportunity to be offended.