Ok, probably only partly.
It would be great if ADHD turned out to have an avoidable (or at least reducible) cause. Seriously great.
Some stuff we still need to know (and the kind of questions you should ask yourself whenever you see a claim about etiology (cause of a disorder) based on a correlational study):
Is it causation: Are kids with ADHD more often from homes with lead-based paint? (Or lots of toys from China, maybe?) If not, that suggests some other cause for higher levels of lead in their blood. For example, they may be more likely to lick the walls. (Not joking – kids with ADHD, at least those who are hyperactive, tend to seek stimulation. And a major cause of higher lead levels in blood is licking lead paint because it tastes good.)
Are there kids with ADHD who don’t have higher levels of lead in their blood: It could be a cause, but not *the* cause. It’s entirely possible ADHD has more than one cause. As a quick analogy, take pneumonia – it’s a condition that can be caused by bacteria, viruses, physical injury… We only have so many pathways in the body (including in the brain), and pathways can be interrupted by more than one cause.
And, of course, does it replicate?