A factoid is, formally speaking, not a small fact, but instead something that appears to be a fact but may be false. Similar to how an android is not really a man, and a spheroid is not really a sphere.
That said, I love the self-referential truth of:
"Saying 'a factoid is a small fact' is a factoid."
It works whichever definition you believe in :)
From Wikipedia: [Factoid] The term was coined originally in 1973 to mean a "piece of information that becomes accepted as a fact even though it’s not actually true, or an invented fact believed to be true because it appears in print." Since then, the term has evolved from its original meaning, in common usage, and has assumed other meanings, particularly being used to describe a brief or trivial item of news or information.