This seems weird. No one disagrees that there are 2 biological (genetic) genders. Gender identity is something entirely else that is being actively researched.
It’s a good example how selective presentation of scientific realities can be abused to mislead.
Chromosomal defects in a binary system don’t constitute a new or between-state, and it also isn’t commonly described that way: XXY (Kleinfeltner) affecting males is the mainstream position.
In humans syndromes that lead to ambiguous (“intersex”) presentation and/or chromosomes are still operating in a binary system, eh Klinefelter affects boys.
The same is true for (very) rare hermaphroditism: in this case both gametes could in theory be produced, in practice though individuals are sterile.
Chromosomal abnormalities would be the modern term, it applies to both sexual as well as other chromosomal abnormalities like Down.
But to answer the question as asked: Yes, it fulfills the definition of the older term.
> Is it a birth defect?