YABU, and ridiculous, and it's non of your business what other children wear.
I can make ds2 (9) wear a coat when he needs to, and on the odd occassions that he doesn't want to, I let him make his own choice. If he refuses to wear a coat, he is the one that feels cold. He will learn the consequenses. On the other hand, there have been times when I have tried to get him to wear a coat, he has said no, we have gone out and I've asked him if he's cold, and he genuinely isn't.
People feel the cold differently.
DS1 has a few sensory issues, and he would much much rather feel a bit chilly than feel uncomfortable with a coat on. And he does find them particularly uncomfortable, no matter how many styles we have tried. He will wear one when it's very cold, but otherwise, he would prefer to just wear a fleece because it's less restrictive. He doesn't feel the cold anywhere near as much as I do, and I have to respect his choice.
There is a difference between being a responsible parent and being a parent who never allows their children to make their own choices and learn from the consequenses of bad choices. I don't want my children to be in their teens and unable to make a choice about what to wear without my input.
Wind your neck in and worry about your own kids, don't worry about anyone else's, they are bugger all to do with you.