In the developed world, people's perceptions have changed.  Most people are 30-40 lbs overweight.  So if you put someone who is 30-40 lbs overweight that crowd, people wouldn't consider them overweight.  They'd consider that average.
The goalpost has moved.  A person with a 23-24 BMI, for example, would've been considered average a few decades ago, but now many people consider that "skinny".  And someone who is 21 BMI, while still in a healthy weight range, would be called anorexic.  People are generally not seen as overweight unless they're morbidly obese.
The % of Americans who consider themselves overweight is the same now as 20 years ago.  Yet the % of Americans who are overweight or obese has gone up significantly.   This means people consider their weight relative to the population rather than in absolute.  Only 25% of Americans have a normal BMI.  3 in 4 Americans are overweight. 
Some will argue that BMI overestimates how fat people are because it doesn't take muscle into account.  This is true for a small portion of the population that actively bodybuild.  But for most people, it may overestimate it.  If you're a 180 lb athlete at age 25, but you become sedentary.  When you're 35 or 45, you may still be the same 180 lbs, but with a higher bodyfat percentage.