Factoid did not originally mean a small fact. When writer Norman Mailer coined the word in 1973, he used it for something closer to a false fact, a claim that people accept because it has been printed, repeated, or circulated.
Mailer described factoids as things that have no real existence before appearing in a magazine or newspaper. In other words, they feel factual, but they were invented or exaggerated.
Today, many speakers use factoid in a newer sense: a brief, interesting piece of information.
- Original sense: That celebrity story was a factoid, repeated until it sounded true.
- Common modern sense: Here is a factoid about octopuses.
Both meanings now appear in real usage, but careful writers may prefer fact, trivia item, or false claim when they want to avoid confusion.