It is possible that the Neanderthals were ‘always’ cannibals, and that when modern man emerged onto the scene into these Neanderthal valleys and realized the hunting practice....they chose to eradicate Neanderthals entirely.
Since the Neandertals are the forebears of most of us, and cannibalism persists right up to the present day -- generally but not always a grim consequence of some kind of food shortage -- no, that's obviously not what happened.
Yeah, but that doesn’t fit the globull warming, Chicken Little narrative.
Could be... or the Neanderthal dined on unicorn until there were no more.
My guess is that when humans came to be the largest “animal” around, the Neanderthals may have taken to catching and eating their sapiens neighbors. We sapiens then proceeded to kill Neanderthals whenever possible except for keeping some of their women.