Depends on what you consider confidence. Most rational men see confidence as the accumulation of experience and success. This however neglects what women and low iq men see as confidence, for example the emotionally unstable, violent gangbangers who will sexually assault a woman at a “club” are considered confident simply because they don’t fear repercussions for their actions. Similar are the men who act like the loudest monkeys to imitate animal hierarchy, it’s a low iq tactic, but is proven successful with women because tingles outweigh reason.

I'm not sure, but it's a very tricky subject. The line of cautious confidence in your own skill is the perfect medium; but below that is both the un-challenged confidence of the ignorant and the over-zealous confidence of the insecure. But then above that line is the arrogance of the smug, and the idiocy and insanity of the truly brilliant.

Then, combine all of that with all the types of people who lack confidence.

There are so many people who are wrongly confident at all levels of intelligence, I would bet that there's basically no IQ correlation to "confidence". But I suspect what they're calling confidence is really just "verbal and physical displays of dominance".

I would assume he's referring to things like the Dunning-Kruger effect where more low IQ types are ignorant but wrong & incompetent while higher IQ types tend to be more introspective & cautious knowing the things they don't know.

It's both. You can develop confidence by achieving goals and basically learning to trust yourself and your abilities. You can also develop it through sheer ignorance. Recall how confidently the idiots told you to trust the experts and take the clot shot.