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".