On its face, his claim sounds ridiculous. Cannibalism is almost always the very last resort of the absolutely desperate, given the strong taboo in all civilized societies against eating human flesh.
Starving people will eat anything and everything even slightly edible before they turn to cannibalism. The Franklin Expedition, the Donner Party and the the Uruguayan soccer team stranded in the Andes are all examples of cannibalism as a final desperate measure, not taken until there was no other choice.
Fortunately, other posters are calling Robertson on his wild claims:
Well, since you can survive 30 days with out food, anyone resorting to eating corpses after 4 days (assuming they waited that long) really belongs listed among the criminally insane rather than the hopelessly destitute. As billions are allocated, thousands of trucks converge, dozens of ships and brigades deployed, and millions of prayers ernestly lofted, I honestly don't know how to categorize anyone to whom this reveals the USA as a monsterous fraud.
Anyone who was healthy enough to loot for TVs and jewellery three days ago is unlikely to have become so weakened by starvation as to consider cannibalism.
Robertson is also raising the vilest of racial stereotypes with his allegations: the black man as bloodthirsty cannibal. Not exactly the wisest thing for a self-styled civil rights advocate to do in a time of crisis!