Perhaps the meanings are not that different if you think about it like this: In latin “confidere” means “to trust”. When you are confident, you have trust in yourself. “To confide in someone” is to trust them enough to tell them of a secret or private matter. If something is confidential it is intended to be kept secret. In other words, it is only for people who can be trusted.

I think confident means to be sure, decided. It can also mean to trust : "I'm self confident" means I trust myself. Confidentially is an adverb, meaning something is secret. Bye !

Confident means an act of trust on something , examples like ' I'm confident on that" .Confidential means intended to be kept secret.

I am not too sure about this myself, but my guess is that these two words have an irregular root. Or, eg: "If my information was being used confidentially, I would be confident."