For some, morality isn't fungible or based on the morality or others (animal or human). If someone is a thief and willing to rob you, does that mean its okay for you to steal from them? It seems reasonable to me to hold a personal code of ethics and standards that isn't dependent (or at all related) to the ethics and standards of others (if any).
Also, I'm not sure a cephalopod has evolved the physical and mental capability to vary its diet on command such that it can choose if it will feed on other animals or not.
At some level humans and cephalopods are just animals, and equivalent in that regard, but I'm not sure I accept the equivalence far beyond that or especially when it comes to morality.
This cannot be how you approach morality. Animals routinely do horrific things to each other. Would you ever ask someone that question outside of a conversation on whom we kill to eat?
I don't think that cephalopods are arrogant when they eat other creatures, although I suppose they may be gluttonous. Why hold yourself to a higher standard than you hold the animals you refrain from eating?