That is not uncommon, the purpose of head shots is not death but is to instant incapacitate the threat. I have seen numerous suicides where the person stayed breathing for days. A young girl in the seventies who survived a hatchet attack to the head lived for years.

Even if trauma does not kill or series injure a person/animal it almost always stuns the subject. It is how we stunned cows in the slaughterhouse before bleeding them out. A pneumatic device was used to stun, but did not kill the cattle.