User blog comment:JonTheVGNerd/PE Proposal: Tantalus/@comment-2059440-20200126093050

a correction however is that Tantalus never ate his son, he served him to the gods to prove they were not all-knowing, when Zeus found out he ordered all the gods not to eat it (though Demeter accidentally ate a shoulder) - Tantalus was punished and Zeus, in a rare moment of charity towards mortals, revived the son and had the gods make him beautiful and prosperious.

Tantalus' son would remain this way for a long time until eventually Zeus got angry because Poseidon was smitten by his beauty, abducted him and took him to Olympus - which prompted Zeus to banish the son from Olympus.

I'd say compared to what Zeus had done to Tantalus however the son was let off pretty lightly (he had suffered enough with a father like Tantalus).

so yes, while a horrible human Tantalus technically is not an actual cannibal himself, rather he's a psychopath who tried to get others to engage in cannibalism for his amusement as he watched - using his own son as "bait".