It is possible the bullet entered the skull and then followed the curvature -particularly if the shooter was firing 'up' at the deceased. Much of the bullet's initial force is expended during entry of the skull (when it punches through bone). The brain is surrounded by cerebral spinal fluid, which is mostly water; water being one of the most effective barriers for bullets.
Small entry hole jammed with boned fragments and gray matter can mean there is not a lot of blood.
Thanks.