Normally this doesn't happen to older dogs, I agree.

What about the man's dogs who was feeding that other food? Are his dogs sick? (Aflatoxin poisoning in food can kill/emaciate a dog too.)

Do those people have cats? The reason why I ask is there is also a weird disease dogs can get from eating cat shit (Toxoplasmosis), but it is also protozoal in nature, like coccidia, and causes a dog to waste away as well.

Jack