That is probably another one of their abilities.
They can distinguish between whose blood can and cannot be consumed. Vampires do drink blood, but not just the blood of any human. Though lesser vampires do not possess what makes vampires the powerful demons they are, the ability of ‘feeding’ is something a few among them are capable of using. ‘Feeding’ is an ability much like the abilities a ghoul possesses, such as ‘Sharp Claw’ and ‘Sharp Fang’.
