Yes, you can have ADHD and be a quiet kid. I was quiet and thought you had to be hyper to be ADHD. This delayed me getting diagnosed until I was an adult.
Sometimes people call non-hyperactive ADHDers ADD not ADHD but officially it’s ADHD-PI which is the primarily inattentive type.
There is still hyperactivity of the brain with thoughts and emotions.
Seek a professional opinion from an ADHD specialist.