An addition to that: Over a decade ago (so unfortunately I have no reference, this just stuck with me for how against common sense it was) I remember reading that being overweight but not obese correlated with good health better than being "normal" weight did. Their theory was that if being sick made it so you were less hungry, you could still get an energy boost by using up fat reserves and be able to fight off illness faster.
This sounds like a much more specific and more testable version of that theory.
There is a problem with the BMI [1] calculation, which is the standard measure used to determine "normal" weight, in that it is dimensionally incorrect. The BMI calculation gives results that are appropriate for those around 5'6" (168cm) in height. The units are in kg/m^2.
The Ponderal Index [2] (AKA the "Corpulence Index") gives values that work for any height, with units in kg/m^3. If you are a young child or over 6 feet tall, you might find the PI/CI works better for you.
This sounds like a much more specific and more testable version of that theory.