In The Legend of Korra S02E07-08 Beginnings, we see how the first Avatar, Wan, came to be. During these episodes, we see him gain firebending, airbending, waterbending, and lastly earthbending from lion-turtles that carry human cities on their backs. However, in Avatar: The Last Airbender, it was established that humans learned bending from various animals. Firebenders learned from dragons, earthbenders from badger-moles, and so on.
In Beginnings, we see humans being granted bending by the lion-turtle when they leave a city. For people on short hunting excursions, this meant they were granted bending while hunting outside the city, then they were non-benders after they returned and the lion-turtle took back the bending ability.
This seems to be at odds with what had previously been established as the origins of element (and energy) bending. Can these be reconciled, or did the writers just retcon the origin of bending?