As far as I can tell, the two words mean the same thing. The other commenter may have meant to contrast with “contagious,” which means that it’s not just possible but reasonably easy to transmit the disease. From the article:

“It is important – imperative – to emphasize that transmissible does not equal contagious. There is absolutely no evidence that people with dementia can spread their disease casually to people around them. Even donated blood appears to be safe, as no association with blood transfusions and Alzheimer’s Disease has ever been detected.”