Everyone does have attention issues
That doesn’t mean you don’t have ADHD.
When I was younger, I could sit and read for hours. Actually, I would sprawl out on my bed and read. And then, I’d either get to the end or just finally come up for air, and realize I seriously needed the bathroom, and something to drink, and something to eat, etc.
It wasn’t healthy.
ADHD means you can’t control your focus, so you might not be able to stop. (I’m sure you know this, but I don’t think he does.) So just because you can sit and read for a long time does not in any way mean you don’t have ADHD.
He just needs education, that’s all. I used to believe the silliest things about ADHD myself. But I got educated, and so can he. If he’s worth educating, that is. If it looks like he’s going to be stuck in his ways and will never change, then maybe it’s time to move on.
Either way, hugs and I hope things work out for you!