True.

But, two thumbs up = 100 and no fingers up at all = 0.

It’s like rolling “1d100” in D&D. Unless you actually have a 100-sided die (a ball with a weight in it so it eventually stops with a number up), you roll 2d10 and declare in advance which one is the tens place (some have a zero at the end of each digit, so that’s tens by default). That gets you 1-100 with no zero option.

So, you’re right that two digits have 100 numbers, 0-99. The dice system has 100 numbers, 1-100. The hand system I described goes 0-100. So technically one of those is a 3 digit number. But, the system allows it and doesn’t (easily) allow any more 3 digit numbers.