Rabbi Dr. Steinfeld

I was talking to MHW this morning about a medical matter relating to one of our kids and I said: "Why don't you ask Rabbi Steinfeld?" MHW pointed out that I called him Rabbi, not doctor, and that she does the same thing all the time.

"Rabbi" Steinfeld is actually "Dr." Steinfeld and has been our kids' pediatrician for over 18 years. He is a wonderful doctor and wonderful, gentle man, whom we trust and admire greatly. But he is not a Rabbi. And he is traditional rather than observant.

What is the meaning of this?