I do agree to some extent, but really the overweight threshold for BMI is 25. And 30 for obese.

At 6 feet / 183 cm that it takes 184 lbs / 83 kg to be overweight. From what I could find, for regular gymgoers the typical weight for people around 6feet is 180-190lbs, which put many people around the overweight threshold. I am myself at 24.9, and while not skinny I am definitely in the skinnier half of the people at my local gym.