The German shepherd runs happily in the park.
Dog runs outside with his owner.
The dog could be running happily in the park with another dog or with another person.  It can't be inferred that he is with his owner.  Furthermore, it's possible the dog is a female dog and not a male dog, in which case, we could not infer his.
The owner of the dog probably not always accompanies the dog
Just because a German shepherd runs in the park does not mean that he is with his owner.