It is just protein .

It's worthwhile remembering that Indo-Europeans had not yet arrived in Europe for another several thousand years in the future. The ice age had ended 11,600 BP and agriculture was commencing in Europe though not as developed as in the Fertile Crescent. This was the age heralding Stonehedge-like constructions throughout the region from Britain towards Malta. As seen in a certain Greek island or more (via a magazine, possibly pre-Greek residual habit) and elsewhere (via TV, somewhere in southeast Asia), ancestor worship did have communities involved in the cleaning and organizing of bones of their departed love ones after a year or two of death to consolidate them and repay their respects. So, I wouldn't jump to the conclusion that they were chomping down on them for sustenance: game was still plentiful despite the loss of Pleistocene great mammals. Only dire survival as in the case of the Andean plane crash some decades ago would oblige such acts.