This story has a point you probably already knew, that dog genes don't vary much between breeds. With free roaming "wild" dogs, though, the genetic structure is much more diverse than purebreds.
When reading this story, I imagined this is probably because of the nature of how many dog breeds were created. The process is brutal, which is why we don't have any new breeds today. Here's how the breeds were created.
Find two or more dogs that have the traits you want in a breed. Get a batch of puppies then kill all the puppies except for the ones that have your goal traits. Then breed those puppies. Again, kill off all the ones you don't want, and potentially their parents as well since they are no longer of use.
When you get some strong traits that you really like, breed father-daughter, mother-son, or brother-sister. This will "lock in" the traits.
The fact that these traits are "locked in" is why purebred dogs have such little genetic variance. Even today, the breed standard for some breeds, such as Rhodesian ridgebacks, recommends "culling" pups with certain undesirable traits. From Wikipedia:
Traditionally, many ridgeback puppies were culled at birth for numerous reasons, including ridgelessness. Contemporary breeders are increasingly opting for surgical sterilization of these offspring to ensure they will not be bred but can live into maturity as non-showing, non-breeding pets. Some breed parent clubs and canine registries have even made the culling of ridgeless whelps a requirement.
And you thought shelters were sad. Think about people purposely breeding dogs and then killing most of the puppies. That takes real... um... well... it takes a special person.