How do you know they got it through being "genetically blessed" and not just...putting the fork down? In my experience a lot of skinny people don't outwardly signal that they're "dieting" because they're literally always dieting.
Being able to easily put the fork down / always dieting is the genetic blessing. Some people maintain a low weight with almost no effort, while the genetically unlucky seem to be hardwired to always be craving food & would subjectively suffer a lot more to eat like the naturally skinny.
I'm full (and would get nauseated if I continued eating) with an amount of food that would leave my sibling still feeling constant hunger pangs... the feeling of "fullness" here is the genetic/hormonal blessing