Look at the surrounding website. What is being sold by Object Mentor? Training, consulting, books, advice. Not software.
TDD != Software
Regarding credentials, we are judging the content on its merits, not deferring to Uncle Bob's authority.
In the same way, software advice that doesn't take the form of deductive argument from mutually agreed-upon principles is largely valuable insofar as the person peddling it is experienced and honest.