factoid
A fact that someone thinks is real, but it's just a guess. It's like a guess wearing a hat and pretending to be a fact.
"I heard the sky is blue because of clouds.", said by a kid who thinks clouds are just colored confetti.
"That’s the dumbest factoid I’ve ever heard.", said by a teacher who’s had enough dumb facts.
"I think it’s true, but I can’t prove it.", said by someone who’s not sure if it’s true.