Diarrhea in dogs can be acute or chronic. An acute bout means that it occurs just the once and is resolved quickly. It may have been caused by eating something that is harmful, such as food poisoning.
Dogs have what I call 'cast iron stomachs'. That is they are omnivores and can eat anything. Anything natural, that is. They can east rotting and decaying meat with impunity. They can eat a purely vegetarian diet, no problem. They can survive on a diet of earthworms in times of scarcity.
Dogs are very adaptable.