cis I think comes from the alps or something, cis/trans-alpine. It's also used in chemistry to determine the handedness of particular isomers (I think). It's a prefix, not an acronym, in any case.
Unless you listen to TERFs (which is an acronym, 'trans-exclusionary radical feminist), who'll tell you it stands for Cis Is a Slur lol

In your example yeah you got it right, cis/trans refers to a gender signifier, whereas homo/hetero is a sexuality signifier. They're similar prefixes with different applications

And then there's me who's just... queer I guess, the more I think about it the more confused I get, be gay do crime and learn to love yourself