This is a normal effect for caffeine. It is a diuretic. Also, my understanding of the different effects you're talking about is that it is only true for people with adhd. Its because people with adhd lack the proper amount of stimulation normally, so providing the right amount of stimulation through a drug will treat the problem without inducing effects associated with overstimulation. They can still experience the same effects that neurotypical people experience when taking stimulants, but they would probably need to take more.

Again, this is just my understanding of it based off of my personal experience as someone with adhd as well as what my therapist has told me. I don't know if its completely accurate or not.