First off; there's nothing suggesting what they're eating is duck. It could also be roast chicken or roast turkey.

Second; in real life there are birds who eat other birds (Which is not an act of cannibalism considering it's bigger birds who eat smaller birds of a different species like how hawks have killed and eaten pigeons) and before you say "But Ducks are in the same family as chickens and turkeys! It's still cannibalism!" no they're not. Ducks are part of the order of Anseriformes, while chickens and turkeys are part o the order of Galliformes. These birds are part of completely different families.

Third; If you're gonna say "But Ducks don't eat other birds!" Well Ducks don't eat cows or pigs either, but I've never seen anyone question Donald Duck eating a hamburger or hot dogs or hams.

Fourth; "But animals walk and talk and are people in their world! They killed a sentient being! That still counts as cannibalism!" We've seen that both anthropomorphic/human-like animals and regular animals exist in this world (As seen with Goofy and Pluto)

Is it confusing? Yes. Is it fucked up? Not really, no.