Social Constructs and Real Conditions
As with most misunderstandings, this is a result of words being understood in a different way than they were intended. To say that disability is a social construct, as that idea is commonly expressed, is not the same as claiming that the underlying condition is not "real." The social construct is not the condition itself, or the label, but society's attitudes toward the people who have it.
Here's an example: I am nearsighted, rather severely so. Before eyeglasses were invented, I would have been regarded as having a major disability, unless I belonged to a small isolated tribe where everyone was nearsighted, in which case I would have been normal. If I lived in a society where people knew how to make eyeglasses, but chose not to do it because they had some cultural reason for believing eyeglasses to be undesirable, I would be disabled. If I lived in a society where people who wore eyeglasses were thought to be less capable of productive work than others and were denied equal opportunity as a result of that prejudice, I would be disabled. As it happens, we have easy access to eyeglasses and contact lenses in our society, and correctable nearsightedness is not considered to be a disability. But it's exactly the same physical condition in all of these scenarios, no more and no less "real."
I could go and get LASIK surgery and be cured of my nearsightedness, assuming that the surgeon decides I am a good candidate for the procedure. I don't have to be cured, though, to participate equally in society with people who are not nearsighted. I simply need adaptive technology, that is, eyeglasses or contacts. There is no prevailing cultural attitude—no social construct—that declares nearsightedness to be a tragic abnormality resulting in a lifetime of exclusion and misery. Rather, it is just seen as one of the many possible characteristics of the human body.
Perhaps one of these days, all of the conditions that are now regarded as disabilities will be seen in the same way.