We must have met very different humans. Are there humans that do that this? Absolutely! Are they in the majority? Absolutely not. Now if you change that framing to "teachers" then I think on average you are going to get more people like that but I've heard many many people say things with complete confidence/certainty that was absolutely wrong. Then again, I've had teachers that have made predictions/statements that they state as facts so I don't know. Dunning-Kruger can account for part of it but still.