Yup. Dementia and brain injuries are both examples of neurodiversity.
Occasionally somebody, usually a baby or young child, will get a brain injury and recover so completely as to be neurotypical afterwards. Kids' brains are very flexible. But, mostly, a brain injury means you are no longer neurotypical. Quite a few things take a human brain out of the typical range; brains vary significantly from person to person.
In fact, it's likely that neurodiverse people make up a rather large chunk of the population. Maybe not a majority, but certainly quite common.
