Everyone commenting on this is confused about large predator behavior. Bears dont have to just win the fight, they have to win EVERY fight with no major injuries for their entire lives. A dog-sized snack is not worth the risk of losing his eye. The dog is not competing with him for territory or food or mates. He has basically no reason to fight it.
The thing is bears are also like this with humans... he really doesnt want anything to do with you
The theory is that if you encounter a bear, you should avoid eye contact and slowly retreat instead of turning around and running. Interestingly, bears behave the same way when they leave