<<- One more thing... Some of what we saw in this episode didn't totally mesh with what we've heard about bending. Supposedly people learned bending from badger moles, dragons, the moon and sky bisons but here, they were given bending. The only way I can reconcile this is maybe they simply honed their existing skills by watching the nature and the rest became folklore.>>
They showed this in the episode. Wan got fire from the Lion Turtle, but in the montage they showed him TRAINING with a dragon to learn how to use it well. So the bending gene was already in humanity from ancient times, but that skill was refined by studying the animals which also possessed the elements. Perhaps there was a time when the art of bending was forgotten after the Lion Turtles left and lay fallow, but it was relearned from the animals.
One of the things I loved about the episode was how they introduced so many new concepts to the mythology while at the same time not contradicting the old stuff and even referencing to it like that. Well done, chaps!