They're probably referring to particular breeds that are known for chronic health issues. Dogs with extremely flat faces (think pugs)? They have a lot of troub

They're probably referring to particular breeds that are known for chronic health issues. Dogs with extremely flat faces (think pugs)? They have a lot of trouble breathing. Also, their eye sockets are shallow and so their eyes will pop out of the socket sometimes. There's a litany of health issues related to chasing the breed standard for dogs, sometimes related to how the standard has been taken to an extreme that deform the dog and sometimes related to the massive inbreeding that's happened as a result of chasing the breed standard. There are certainly some dogs that can live in the wild, and there are certainly some breeders who try hard to be responsible about how they breed for the standard and how they breed their lines together, but the average purebred dog is not one you can just drop in the woods and it'll go find its own food and survive.