There are a lot of examples of the differing meaning of a smile when you google it. Sometimes it is simply not appropriate to smile. I'm not sure if there are any culture that sees them as entirely evil, but a few do have a concept of an evil grin, a concept that sits alongside the smiles being friendly. It doesn't seem to be a stretch that a mistimed smile might make you look like a loon and other such differing beliefs.
https://www.theatlantic.com/science/archive/2016/05/culture-... https://blog.allpsych.com/smiling-means-different-things-in-... https://www.translatemedia.com/us/blog-us/the-meaning-of-a-s...