The normal range of BMI is based on people who are out of shape, or at best relatively lightly muscled as comes from having, say, a sedentary job and doing aerobic exercise which doesn't build large muscles. I'm 6'3" and 190 lbs, and although my BMI is just within the normal range, I still consider myself fat, due to the visible roll of fat around my abdomen. I will continue to watch what, and how much I eat, and try to exercise vigorously more often to see if I can eliminate it, and not worry too much about what the scale says. At least I'm not 230 lbs like I was until June of last year. That weight reduction was achieved mostly through changing my diet, and is an indication that my body type is naturally fairly slender but that my atrocious diet (too much, and too many of the wrong things) had forced my weight up.
Anyhow, I don't disagree with the article and am not surprised that obese people tend to think they eat healthy and exercise vigorously. It's classic victim mentality.