Yeah, it's very subtle. He's essentially saying that the TDD approach has made his code is flawless, and he is incapable of producing bugs.

That was subtle? Perhaps the attempt to be subtle was made too subtly as I can't fathom how it could be read otherwise.

Ahh.. I must lack some sense of humor.

Don't worry, you're not alone. I, for one, congenitally lack a sense of humor myself.