The difference between disease and disability one way of understanding the different ways people approach disability. People who subscribe more to the Medical Model … who focus on treatment, rehabilitation, and finding a cure … think of disability much as we think of Cancer, Leukemia, or Malaria. Most disabilities aren't like that, though. They are social identities, imposed from the outside, and they are more or less permanent conditions that are a part of us.
There are gray area conditions that are a little bit disability, and a little bit disease. Multiple Sclerosis, ALS, and some kinds of Muscular Dystrophy are progressive and can be life-threatening. But they’re not infectious, and on a day to day basis act more like a broken hip than Influenza. See also: Alzheimer's Disease and Down Syndrome.
This helps explain why so many disabled people talk about “fighting,” “beating,” and “overcoming" their disabilities. If you view it as an invading force, it makes sense. And in general, people are more familiar with illness than with disability, so the language and mindset are right there for easy access.