No one is "binary". Even the voltage levels inside electronic circuits, that everyone calls binary, are not binary. What's up with this contemporary obsession for seeing everything in pure black-and-white terms and dismissing the power of the rare, mysterious and unknown liminal states of being, acknowledged since time immemorial by countless traditions?
They observe that in the world around them (media, etc.), “gender A” implies X, Y, and Z traits, and “gender B” implies W, R, and T traits.
The subject does not feel they exhibit exclusively X Y and Z traits nor exclusively W R and T traits, but rather some mixture of the two.
The subject then has two options. Reject the worldview claiming A=>XYZ B=>WRT, in flavor of a more dynamic classification scheme; or introduce a new category, C, which maps to their experienced subset of XYZWRT.
I’ve seen no evidence to support one approach being more valid than the other.