God bless.
This is not the case. He is a Catholic by his own admission.
Steve Brandt, the author of the article, includes an anotated bibliography on his website with the following autobiographical note:
Catholicism and Fundamentalism by Karl Keating
I read this book years ago because I wanted to understand Catholicism better. Should I regard it as Christian or as a Cult? That was my question. When I was halfway through the book I began to feel good about Catholicism. In fact, it was much less weird than I had thought. By the time I finished, I was scared. I was afraid that Catholicism was the one true Church - a position I eventually decided to accept.
PhD training has taught me to check sources. Why did you conclude he was NOT a Catholic???