Medieval citations of non-Muslim/pagan Blacks as inhumane and uncivilized cannibals are not attested by real explorers, and should not be taken seriously. You definitely have read of Ibn Khaldun saying that blacks below Sahelians are all kinds of things, or other random arab historians despising the “zanj” (usually used for Sub-Sahel blacks). All these claims however come from Sahelian (especially Mande) merchants who took advantage of their ignorance of the African interior & sought to prevent foreigners from finding alternative access to these sources of their wealth. Stories of cannibals and monsters inhabiting the goldfields may therefore have served to discourage outsiders, successfully exploiting North African credulity and cultural prejudices. I’d say that this was successful until Europeans like Portuguese & Danes started trading directly with the coasts. It was incredibly detrimental for the Western Sahel.