If there is no interest in establishing what caused the attack, then there is no interest in preventing recurrences with other dogs, and no lessons will be learned.
An enquiring mind looks at the full circumstances of the case - dog's past history, dog's breed, dog's health, what happened in the last day (eg was dog fed and exercised), what happened immediately prior to the attack (actions of both the victim and dog), if that dog and specific child had a history, why the dog and child were left alone together etc etc
It happened at 5am, when you would normally expect both child and dog to be fast asleep. Clearly whatever happened the dog went far too far. It is not, however, victim blaming to suggest that the child did something that prompted the attack. For instance, the child could have acted very reasonably by getting up in the night to go to the loo. He could then have accidentally tripped over the sleeping dog in the dark and fallen on top of it, prompting the dog to think it was being attacked and to attack back, clearly taking it far too far. The child, in that circumstance, would not have done anything wrong but they still did something that prompted the dog's attack.
Truly unprovoked dog attacks are incredibly rare. However, what an individual dog considers to be provocation will vary based on past experiences and may not be considered reasonable by the humans around it. As an example, if you walked through the front door of a dog that was seriously terrorial you could be bitten - the human has acted reasonably (if invited in, not a burglar) but the dog considers itself provoked. Alternatively a dog in possession of something that it considered very valuable (eg a raw meaty bone) and feared the human was going to take it away might attack to defend the valuable item.