The issue with *factoid* is that it doesn't necessarily mean *false*.

Definition of *factoid*:

> 1. A brief or trivial item of news or information.

> 1.1 An assumption or speculation that is reported and repeated so often that it becomes accepted as fact.


I think the word *misconception* fits in your sentence:

> Because he researched what he had heard from his friends, he was able to refute many of their *misconceptions*.


*Misconception* does necessarily mean *false*. Definition:

> A view or opinion that is incorrect because it is based on faulty thinking or understanding.

Example:

> Public *misconceptions* about AIDS remain high.



A *myth* is similar. Definition:

> A widely held but false belief or idea.

Example:

> He wants to dispel the *myth* that sea kayaking is too risky or too strenuous.



More synonyms include:

> error, misbelief, miscalculation, false impression, fallacy, false notion, old wives' tale, urban myth/legend




(Oxford Dictionaries Online: [factoid][1], [misconception][2], [myth][3])


  [1]: http://www.oxforddictionaries.com/us/definition/american_english/factoid
  [2]: http://www.oxforddictionaries.com/us/definition/american_english/misconception
  [3]: http://www.oxforddictionaries.com/us/definition/american_english/myth