i would guess the author does not understand the differences in meat from herbivores, omnivores, and carnivores if the wyvern meat is described as "exactly like wagyu beef"
from my limited understanding, iirc any introduction of meat into an animal's diet makes their own meat significantly more gamey, and is therefore more difficult to cook with as the average person simply does not have enough experience.
I mean, I do think I'm correct to assume that a Wyvern's diet will not consist of only plants. Additionally, I might go so far as to theorize that Wyvern meat might share many similarities to the meats of bird of prey. But, seeing as I can eat neither of these, it is all supposition.