The fact of the matter is, most people are cisgender (even if they don’t identify that way).
The entire story this quote comes from is written from an academic perspective that describes general population phenomena, not individual identities. Identity is not the only component of gender, thus a person’s subjective identity is important, but it’s not the only aspect of their gender. From an objective, general perspective, I stand by this statement: those whose gender identities align in socially-expected ways with their gender assignment at birth may be described as cisgender. However, they probably don’t identify as such. (Most cisgender people don’t identify as cisgender. They identify as women and men.)