If you’re looking for answers, I’d say look at the studies yourself. Do some research, but take everything with a grain of salt. Personally, I don’t think screens could possibly cause a major neurodevelopmental disorder with what seems to be genetic influences. You’re right about adhd kids seeking stimulation, though. Many of us love games and TV and other stimulating screens. But if screens directly caused it, the entire generation would have adhd.
If you want a personal example, my little siblings are only 3 years apart. They’ve been raised almost identically, and both spend a lot of time playing video games. The older one has shown signs of adhd since he was very young, and it became very obvious once he started school. He is now 10 years old and is undergoing formal diagnosis. My little sister, however, is vastly different from my brother and I. She has an astounding ability to focus, and already displays executive functioning skills that took me years longer to develop. She doesn’t forget things, and consistently reminds my brother and I of what we we’re doing, and she’s only 7! We’re pretty confident that she doesn’t have adhd. However, she’s spent just as much time as my brother playing games. Perhaps even more, because she finishes her homework much faster!
I personally think adhd is greatly influenced by a genetic component, but we don’t actually know what causes adhd. There is no proof that screens don’t cause adhd, but the likelihood of TV being the reason you and your son have adhd is negligible. You probably aren’t responsible for your son’s adhd, except perhaps by providing some of the genes necessary to develop it. Don’t feel too guilty. ADHD is a part of your lives, and, in this day and age, so are screens.