Cisgender and transgender are different than sexual orientation (gay, straight, or otherwise). A cisgender person is a person whose gender identity aligns in expected way with the sex they were labelled at birth. If you were labelled male at birth and you grow up to identify as a man, you are a cisgender man. Cisgender and transgender people can have any sexual orientation.

Perhaps you heard ‘sis-gender’ or ‘sissy-gender’ when people used the word “cisgender.” Or thought it had something to do with being a ‘sissy’ (an effeminate man). It doesn’t.

In the other piece you commented on (“Are Gay Men Cisgender?”) I argue that gay men aren’t necessarily cisgender. We don’t all identify as men and we can’t know if we’re all biologically male. Unless those two things align, a gay man isn’t cisgender. (BTW I’m in the minority on this point.)