Self-confidence is the product of accurate
knowledge.
Or delusioned knowledge (Read; Thinking one knows, or thnking one is ...........
While in reality it isn't/your'e not that good/smart/skilfull/etc.....)).
All suffering and fear is created by a fundamental
misunderstanding of the true nature of Reality.
Buddha said that a good many years ago.
I 100% agree with your quote.
People with "delusioned knowledge" in this context, I would say are people misunderstand their true nature, and substituted it for a false nature which they offcourse percieve to be the real nature.
To add, some people have a big ego. And thus appear (very) confident at first sight, since they derive it from their perceptions of what they are, achieved, postition in society and/or the skills/competences they have. But a big ego, often is a fragile ego I found. Because if they loose their postition/status in society, or someone questions their past achievements or they do something where the result doesn't fit in with the view they have of themselfes. Or if something happens that is their cause/fault, they often become super defensive becasue they can't handle an hit on their ego, or what the persona they created in their head that they themself are.
And imo, confidence derived from knowing your true nature. Is more unshakable. And holds firm, and doesn't feel attacked or deminished. Whence faced with crtisism, failing at something or whatever.
In the face of failure and/or cristisism, one can most easily seperate the self-confident from the not self-confident.
At least, that's my opinion and experience.