Humans face a number of challenges when driving. Cars, roads, laws, traffic systems, etc. have all evolved to help them meet those challenges, but it is all shaped by our expectations of the humans. When a human doesn't perform to those expectations, we say it is their fault. When an accident occurs despite them meeting those expectations, it's not their fault.
But folks with ADHD have brains that don't match society's expectations; cars, roads, laws, traffic systems, etc. have not evolved to help them. Their brains are effectively a chaos factor for all the safeguards we have in place... Even their advantages can be disadvantages because everything was designed to help someone who didn't have them.
Even if an accident wasn't their fault, I think it's quite credible that people with ADHD might just be more likely to be in situations where there is a higher risk of an accident... and I'd expect it'd be more common for accidents to be their "fault", because again, how we determine fault is defined by expectations they conform to.