He's the head of the vamps.
They waited for Xander to return with the three vamps trailing him.
The kid was hard to read, and she guessed his anger had more to do with his struggle to understand his new role than the vamps who clearly had no respect for him.
She drew the gun at the small of her back and aimed it at the head of one of the vamps.
One of the other vamps drew a weapon.