Do you find it rude when a random guy tells you to smile?

I remember reading about women being angry when guys told them to smile. Today I was browsing at the grocery store and a random guy stood by me a little then said "you should smile" when walking away. It didn't really offend me I was just confused why I was apparently supposed to be more cheerful when picking out some crackers?

What's the point of telling a stranger to smile? 😕