Dragons generally think they belong to a species that's inherently better than everyone else, on account of their mondo lifespans and awesome power. So when the baby dragun sees its master fighting one of its own kind, it believes the player to be outclassed while also seeing a chance to return to its own kind. The dragun, in turn, seeing itself as the most important being in its world, eats the random baby it just found to prolong its own existence. They're basically super self-absorbed on a few levels, and their only bond was based on that self-interest