The commenter your responding to is most likely using "gender" to refer to the concept you would describe as "sex". That is, the biological characteristic of being male or female rather than a grammatical concept.
A trait either is binary or is not (being binary is, itself, binary.) A trait that the vast majority of the time takes on one of two values, but other times takes on other values, is not binary.
Even if that was the exact set of possible values, that's not binary (though I suppose if someone overexposed to SQL might mistake it for a being binary...)
