It's both. There's a whole school of thought about ADHD as an adaptation to hypersensitivity/trauma. See: Gabor Maté.

Edit: there's also the fact that an ADHD diagnosis increases the likelihood of an anxiety disorder diagnosis, statistically. They tend to go together. I can't remember where I read it now but some clinician or researcher recently estimated that up to 75% of adults with anxiety disorders may also have ADHD.

That's my secret cap! My undiagnosed ADHD was the source of my misdiagnosed anxiety and depression!