Personally, I suspect it's autism rather than ADHD (and Inattentive-type ADHD, AKA: ADD). In my experience the people I've known who have just ADHD tend to be better at filtering out external stimuli than those I've known with Autism. And likewise the folks I've known who have both ADHD and Autism tend to have a harder time filtering out stimuli, or getting distracted by particular stimuli, than those with just ADHD.

That said, my own personal (and very unscientific) theory is that ADHD and Autism are merely differing manifestations of the same neurological phenomenon. So I could see that somebody who has ADHD might be more sensitive than a neurotypical person.