My guess is it's like the situation where when a person is bit, they become a vampire slave, more zombie like. So I would guess the master vampires or whatever is human Esq, those killed/minions are monsters.
Also, yall gotta stop whining about "so long to elegant vampires." Clearly there are other vampires who are not monsters, Gabriel is a Belmont, Drac is practically conformed, so is the VK. Why are you still complaining??? There have been PLENTY of buff, monstrous, demon like bat beasts throughout Castlevania.