But it's actually not just being "overfat".

It's specifically a high level of visceral body fat.

Genetics determines which parts of the body gain fat first as you gain fat overall, and some people have the unfortunate genetics to gain it first viscerally and some people have the fortune to gain it there last (and everything in between).

This means that you can have different people with the same body fat percentage but drastically different disease risks.

But yes this was also known already.

That's why it's been recommended to take a waist measurement alongside BMI to get a much more informative screening tool. Waist-to-height ratios are another alternative.