The two examples of impaired writing are pretty bad. I would consider anyone who wrote like that already impaired, but according to the article the people who wrote that way presented as normal. That hardly seems possible.
I reviewed the article, but couldn't find the exact wording of the question that was presented for the participants.
This is all I could find:
As part of it, they took a writing test before any of them had developed Alzheimer’s that asks subjects to describe a drawing of a boy standing on an unsteady stool and reaching for a cookie jar on a high shelf while a woman, her back to him, is oblivious to an overflowing sink.
What I'm wondering is "how clear was it made that the answer should be in essay-writing format?"
That is, if someone gave me that drawing and asked me to "describe it" - I may very well make some point-form notes as in the "missing auxiliary verbs, articles, punctuation" example.