20% said they would require 100% certainty, which is equivalent to stating that not even the most obviously guilty person in existence deserves to be convicted. I'd posit that this is more so evidence that the general population's knowledge of probability is abysmal.

Or their concept of “certainty” or “doubt” is different from yours.

I'm not even sure what that is really supposed to mean. If 100% precludes the potential of an event with infinitesimal likelihood (mass delusion, possession by ghosts, etc.), then as I said nobody ever gets convicted.

Otherwise, any "concept of certainty" that uses "100%" to refer to something that might not occur, is either gravely misusing mathematical notation or self-contradictory.

While technically correct this is obviously not how people speak. If you ask someone 'what is the percent chance that drinking this glass of water I just got out of the tap in New York City will kill me within a few seconds?' They would respond '0%', even though by a mathematical definition that is not true.

People generally consider context for their choice of words. Alongside 100% they were also given options such as 99.9999999%, it's clear that 100% in this case is not just used as "very likely".

Can you statistically evaluate such a thing? Its all black swan.

If you look at it in a bayesian way this is not an issue. "I can't put a number to it" would definitely be a legitimate answer, but "100%" is just wrong.