It’s the original meaning of the word, coined by Norman Mailer in 1973.

The second definition in your quote confirms that factoid can mean a widely-accepted false fact.

(2) something fictitious or unsubstantiated that is presented as fact, devised especially to gain publicity and accepted because of constant repetition.

From here:

On occasion, a writer will coin a fine neologism that spreads quickly but then changes meaning. “Factoid” was a term created by Norman Mailer in 1973 for 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. Mailer wrote in Marilyn, “Factoids…that is, facts which have no existence before appearing in a magazine or newspaper, creations which are not so much lies as a product to manipulate emotion in the Silent Majority.” Of late, factoid has come to mean a small or trivial fact that makes it a contronym (also called a Janus word) in that it means both one thing and its opposite, such as “cleve” (to cling or to split), “sanction” (to permit or to punish) or “citation” (commendation or a summons to appear in court). So factoid has become a victim of novelist C.S. Lewis’s term “verbicide,” the willful distortion or deprecation of a word’s original meaning.