XXY is Klinefelter syndrome. By definition it's a condition where boys and men are born with an extra X chromosome. Their sex is male because, also by definition, the presence of a Y chromosome means male.

The term “birth defect” fell out of use because of its stigmatizing word construction.

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?

Yes.