It needn’t have been anything physical, like her fitness level or body shape, nor about her age. It was probably just a look that didn’t suit her. That happens. Maybe it was something that jarred just your personal aesthetic, or perhaps it would have jarred lots of people. The point is, it’s no good projecting that into yourself. There’s no way you can make such comparisons.
I certainly don’t think you’re delusional, or if you are then I happen to share the same delusion as I think you look quite presentable in heels, always thoughtfully put together - and I say that as someone whose own personal tastes do not run to sandals or pumps.
telling someone they are delusional in terms of their style or appearance and its affect on others is undermining and cruel. And irrelevant as the only opinion that matters in this situation is you. If you like the way you look, or how it makes you feel that’s what matters.
And the same with the woman in the boots and shorts. If that look expresses what she feels about herself or wants to say, that’s what matters.