There were some major differences between dragons and wyverns. First was size, dragons are massive beasts while a wyvern was a little bigger than human to small horse sized. Other than that it was their appendages and wings, while dragons had all four legs and a distinct set of wings. Wyverns would have wings attached to their arms and to the body, and legs.
Af for other than appearance dragons were intelligent creatures and capable of using their own magic and blessing other creatures. Wyverns did none of those things and were much more wild. They had the intelligence of perhaps a dog. They wouldn't be able to use the translation spell on them.
The goblins had extensive knowledge from scrolls and other transitions about their prey. Wyverns were always a topic that goblins discussed. Other mounts as well but every creature that can't fly somewhat always wants to be able to.
