An EEG cannot and does not show if you have ADHD. There are no biological markers that show you have ADHD, which is why it’s done like a psychological evaluation- they have to go based in negative symptoms.
You will have been given the EEG to ensure that you do not have epilepsy, which ADHD meds could REALLY screw up.
In Norway (where I got Diagnosed) I had blood work, EEG, EKG, and a CT scan to ensure that meds wouldn’t cause me harm. Same thing as you.