Because it is written In the article. The whole article is about the fact that the observed symptoms hint at cerebral amyloid angiopathy.

From Wikipedia:

Cerebral amyloid angiopathy (CAA) is a form of angiopathy in which amyloid beta peptide deposits in the walls of small to medium blood vessels of the central nervous system and meninges.

Also Wikipedia:

Pathogenic amyloids form when previously healthy proteins lose their normal structure and physiological functions (misfolding) and form fibrous deposits within and around cells. These protein misfolding and deposition processes disrupt the healthy function of tissues and organs.