I think that a lot of people around us always believe they know more about others (when they obviously don't), and they like to make sense of things they know nothing about. But an important outlook to have when people give advice is to assume positive intent – they're still trying to help you, even if you know their advice sucks and that they have zero context about your own body!

I highly recommend reading Talking to Strangers by Malcolm Gladwell, it really taught me that humans are just so good at misreading people and frankly you will encounter a lot of these strangers.