I'm really not convinced of this. They may eat a lot of junk food, but huge amounts would need to be checked. They probably eat smaller portions than overweight people
I would be one of those people that others assume can eat what they want, in huge amounts, without exercise.
Truth is I can/could do that, for a period of time that's probably longer than other people could.
In reality I do loads and loads of exercise most of the time but sometimes I go on holiday for a few months and I don't do any exercise and I drink every day and I eat like a horse every day and I can do it for a few months with zero change in outward appearance or significant effect on the scales.
But I can't do it indefinitely. The people who see me when I'm on holiday probably think I'm a mutant
However the most overweight person I know eats effectively what I'd consider a meal for 2 on their own, pretty much every meal. Even when he's on a health tip his portion size is eye watering, a huge bowl of porage, with nuts, fruit, honey, 2-4 slices of toast with spreads, a yoghurt, a banana and you're looking at all this stuff and thinking how many people is this for? And he couldn't understand that, he couldn't understand why anyone would stop at a bowl of porage, when there's all that other food that needs eating
He's still really overweight, unsurprisingly, sometimes he loses more than my entire bodyweight during a health phase
Had a previous partner when I was young that when she cooked dinner used to cook 2 chickens as standard, for 2 people. She used to eat chicken cos it was healthier than other meats in her perception but she could not perceive that this did not mean you should eat a whole chicken every day to stay healthy