From that, wild conjecture.
How do we know "great sleepers" express only more of the better proteins? I could just as much theorize that better sleep leads to more proteins which could lead to more deposits.
Did they control for cognitive function? We know that different people need different amounts of sleep to function properly. How do the patterns shift for a long sleeper vs a short sleeper.
My general approach is to tease out the facts and go to the original source. As an ex-neurosceintist, I often get irritated at the "sciencey press" that follows.