Indeed, not everyone with ADHD is going to have the same reaction to caffeine so it may not be the strongest correlation. I did look into it in the past and for a number of people with ADHD it has an opposite effect of what it does for other people.

For those folks, it won't give them a burst of energy unless they drink a lot of coffee and a smaller amount can conversely calm them down. Caffeine works through a separate neurotransmitter process than ADHD meds (it blocks adenosine receptors whereas adhd meds boost dopamine and norepinephrine) which may be helping some people by lowering neuron stressors which incidentally helps relieve ADHD symptoms.