"That doesn't mean he then has to demand the dog is pts"
Yes he can and yes the law says he can. Why is this so hard for mn to understand. A child has been bitten, on the face, the favoured area for aggresive dogs, under circumstances not witnessed.
The Veterinary Journal published a study a couple of years ago regards facial bites. The group studied were all children. 79% were leaning over, a further 19% were putting their faces close to the dog.
Not one occasion of facial biting followed an incidence of pulling at the dogs skin, tugging the dog, tripping over or falling on the dog, during feeding, nail trimming, or interactions posters here expect. None. Also in 75% of the cases studied, the child was known to the dog.
What this doesnt mean is that, 79% of dogs in the population, will bite if you put your face near theirs. It means that 79% of dogs who acted aggresively in this manner, did so prompted by mere approach. Those dogs, just as the OP has described hers, are and will continue to react aggresively by mere approach.
Luckily it is a very very small number in the canine world who respond in this way, but when identified, must absolutely be PTS due to the fact its is guaranteed to re-occur. This is how this dog reacts when approached at close quaters. Facial attack.
To continue with the 'poor dog' response, utterly ingnores what has happened here, and blames both the child and the OP/owner (who I dont blame, my issue is with the response as to what to do about it).
It is squarely on the dog, and no its not 'normal' and excusable behaviour.
www.sciencedirect.com/science/article/pii/S1090023315004189