I know plenty of people with ADHD diagnosis and normal childhoods without any unusual trauma. Most of them also have comorbidities (stuff typical to autism spectrum, learning or motor function difficulties).
I think ADHD is something you are born with, but there are many other things that can cause similar difficulties, including trauma. And as the linked article mentions, neurodivergent children are more likely to have parents who suffer from similar difficulties, which may increase their chance of suffering some sort of childhood trauma.
I also thought I had a relatively normal childhood but it turns out those long episodes of terror and anxiety at home and school, later repressed through a slew of coping mechanisms, were -if perhaps "normal" enough- definitely not healthy :)
Likewise, but also I've got boy-girl twins. They're 9 now, but we're pretty sure we could tell he had ADHD at six months old (on a waiting list to see if he's autistic too). She's never shown any sign of either. As twins, they've been raised together, I can't think that he suffered any more trauma than she did.