That sounds intuitively right, but that this might not be the main cause. Fried potatoes (french fries and chips) are causing obesity, which in turn causes diabetes. They also are high in carbs, though not sugar.
Arguing about sugar vs. fat gives the food industry an opening to say "the science not in yet" and do nothing. Spearing this kind of uncertainty is their favorite PR strategy.
An experiment: go to the pet food aisle of a grocery store, and try finding a dog treat/biscuit that doesn't have added sugar.
Treats labeled as "chicken" or "bacon and cheese" have sugar as the second, third, or fourth ingredient.
Sugar is omnipresent even in pet food.
It is strange that bread has sugar in it now but it's typically a small amount like one gram per serving: https://saraleebread.com/our-breads/classic-100-whole-wheat-... It does make snacking more harmful though, as a blood sugar spike can be added where not expected.
The comment they replied to literally says "(refined) sugar". They are talking about added sugar, not the constituent molecules of the food.
They’re not good for you, but I’d argue they’re not as much of an issue because you can avoid fried potato products much more easily than sugar.