I wouldn't blame the smell of blood, the smell of chicken would attract anything attracted by blood long before they smelt that. Not to mention hawks hunt more by sight so movement than smell.
The hawk might have been attracted to the commotion and a body? I wouldn't assume that's what it was, they are more likely to pick them off one at a time over a week or so than wipe out a whole flock in one go and after attacking one the others would have scattered and hid so not been continuing easy targets. I would be searching for signs of four legged predators or if it was the hawk the others could still be in hiding so keep an eye out tonight some more may come home at bedtime hopefully
So sorry to hear you have had such an awful thing happen.