You are right. It doesn't make sense. How was it tested? At a doctor's office? It almost sounds as if your equipment is off. I'd have it tested elsewhere.
It was done both with calipers and a hydrostatic tank at the kiniesiology department at my college, by the teacher who was using me as an example for their students. He was surprised by the results as well, and had another teacher double check. I bench press 150 pounds and leg press around 400, and have done this for around 13 years. They finally came to the conclusion that I was one of those people the BMI does not work for; but I have never yet found ANYONE it does work for. As for how I look, my rib cage is 40 inches around and every single rib is visible. My wrist is 7" and the bone is clearly jutting out. I'm half Native American, so I wonder if that has anything to do with it.
Oh, that explains it. You are extremely fit. Muscle weighs more than fat. Your weight is what it is because of muscle.
I'm not generally on this site - I write for Alzheimer's and saw this question. Somehow, health and fitness got put in my queue - so forgive me if I'm out of my depth. But this is an interesting question. I think you've answered it yourself and should congratulate yourself on your great physical fitness!
Carol from OurAlzheimer's