This is exactly the wrong interpretation. We know that cannibalism causes prion disease, and we have known that for as long as we have known about prion disease. the question is not whether cannibalism causes prion disease, which it definitely does, but whether past cannibalism was common enough to have selected for some innate resistance to it.
http://www.virology.ws/2015/06/12/resistance-to-prion-diseas...