The issue with factoid is that it doesn't necessarily mean false.
Definition of factoid:
- 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, misconception, myth)