It’s not a universal rule at all. I know people who are very ADHD who if they drink coffee they have a panic attack. I know people who it makes tired, and I know people who it makes productive. Personally it makes me more talkative.
Basically, it’s not a criteria for diagnosis at all. Everyone’s brain chemistry is different. There might be a higher percentage of people with ADHD whom caffeine does not affect compared to the general population, but that does not at all mean that to be ADHD you have to have that same thing.
Can we make an exception for Vermin Supreme