Amyloid-Beta is a specific instance of amyloids, while prions are a class of amyloids:

>"Some amyloid proteins are infectious; these are called prions in which the infectious form can act as a template to convert other non-infectious proteins into infectious form." https://en.wikipedia.org/wiki/Amyloid

So if amyloid-beta is determined to be "infectious" (however that is done) then it would be put in the prion subclass of amyloids.