“most” would be an exaggeration, but many are. Other animals commonly used in placeholder names are also horse, chicken and lion.

Pig was just the most common meat animal, so any unknown animal that you’d eat would he called an xyz pig. Apple was also used like this for all kinds of fruits and vegetables:

orange = Chinese apple

tomato = golden apple (?)

pomegranate = granate apple

potato = earth apple

jimsonweed = thorn apple

And so on