That doesn't make him an idiot, it just means he watched some TV.
A lot of people think the Jews in Egypt built the pyramids, but they didn't.
This doesn't make them idiots.
(For anyone who doesn't know, the pyramids were there before Josef arrived.)
People aren't required to know everything, and when they don't that doesn't make them idiots.
Speaking without knowing something also doesn't make you an idiot. (If that was the rule the entire planet is nothing but idiots.)
The general issue is that people don't realize when they don't know something correctly, and it's impossible to vet every single thing you hear.
You can call him an idiot if he was corrected, and despite evidence he refuses to change his position. Has he done that?
Not knowing something isn't what makes them idiots. Spouting off about it as though they do is what ruins their credibility. At the very least it demonstrates that they're bad at vetting their sources.