I find it hard to believe a dog turns aggressive on being startled.
Dogs don’t get easily spooked.
The dog was already uneasy and ready to strike with new baby there in his face. The cough and the dog was on already high alert to engage strange new being. No adjustment time for dog and brainless self absorbed parents.
I'm sure it can but probably rarely. I think sudden unexpected sounds can even cause humans a fight or flight reaction while sleeping, resting etc.
The dog might well have been ignored and neglected with a newborn in the house, and taken the infant as a threat. Sensible parents go through a very careful process to help the dog adjust, just as they would with other children.
It’s the breed. Sheep dogs herd sheep, Hunting dogs track prey, Pit bulls show random aggression. There is a reason many communities have a ban on owning pit bulls. Animal shelters are full of pit bulls nobody wants. They have been bred to be aggressive. Yes as previously posted, they are a ticking time bomb.
Believe it. Seen it first hand many many times. Sudden sounds can initiate destructive violent dog aggression in those dogs with behavioral problems