I think the answer lies in your question. We have not observed such behavior (conscious dietary preferences), but that says nothing of capability.
Opting out of meat is only really possible for us because of farming. Other species lack the physical capabilities to farm as we do. Nor can they communicate to us the depth of their cognitive capabilities.
Rejecting human exceptionalism is not the same as saying we are indistinguishable from non-human animals (which would be absurd to argue), rather that our distinctions do not make us inherently more worthy.
Opting out of meat is only really possible for us because of farming. Other species lack the physical capabilities to farm as we do. Nor can they communicate to us the depth of their cognitive capabilities.
Rejecting human exceptionalism is not the same as saying we are indistinguishable from non-human animals (which would be absurd to argue), rather that our distinctions do not make us inherently more worthy.