I sneeze when the sun gets in my eyes. This may be one of those useless mutations though.
Horomones can stimulate reflexes, and conditioned responses to the premise of hunting likely provoke not only an adrenaline response, but other secretions, as part of coordinated psychological and emotional activity at the begining of the fight-or-flight routine.
Sneezing is a reflex, and there's probably some hereditary cross-over in the genetic mix that provides for the complex of neurological signaling.
If there's some interplay with group activity, maybe it's demonstrative of a pattern of emergent evolution for a brand of pheremone to jump the air gap between peers, reinforcing a pattern of hunting success as part of a feedback loop, when combined with the canine sense of smell?
Does the author really think humans used to sneeze on demand?
Edit: made myself sneeze, took about 7 seconds.