It’s like everything becomes “evidence,” so what can we say is actual proof? Everything is conditional. But it is a playful, circular and clever bit of reasoning: “absence of evidence is actually evidence of absence.” If you take it to its logical end you end up with skepticism or maybe cynicism.
No, it’s not clever, because it’s wrong. Absence of evidence can exist in any situation, whether the contested thing happened or not.
That’s logic.
The statement is not clever, that was the CIA guy’s point, and it’s not even circular in the logical meaning. It just has the word “evidence” in it twice. That doesn’t make it circular.