For the ethics of omnivory in general, I'm with the Buddha: if you didn't kill or otherwise cause the death of a specific creature, you've done no harm. You can't do harm retroactively by eating the flesh of something already dead.
Pretty much the most ridiculous argument I've ever heard.

Of course you caused it to die. Do you think that the food industry produces a fixed number of animals each year and if people don't eat them then they just rot..? No, you demand more meat, so the supply increases, so they kill more animals. It's entirely your fault.