It doesn't make it true. It does however make it the most logical assumption.
Why, Faith? Why assume anything ,when there is absolutely, no proof?
No body has been found and although the handler in this case has said …….in paraphrase:-
The alert is indicative of cadaver scent ,but has no evidential, value without other corroborating, evidence.
There are many reasons why a dog may alert, when in fact there is no cadaver or cadaver scent in the vicinity.
This does not mean that the dog is not doing his job as efficiently as he was trained. Many things can cause the dog to be inaccurate in what is expected of him, but he can only indicate what he has been trained to find and can not be expected to differentiate between cross contamination and the other causes of false alerts by the dogs.
Therefore it is highly possible there has been cases of a dog alerting when the missing person has been found alive, but why would we ever hear about it?
These dogs are only deployed when there is a strong possibility of the missing person being found dead, often in suspicious circumstances. We will then hear about the dogs alerts….if there were any, when the victim is found.