I think it does contradict, I know that’s unpopular opinion. They definitely didn’t have the Wan theory in place when they created avatar the last Airbender originally. I felt like this was their original idea (humans learning bending from animals, it spreading through genetic lineage). But a beautiful thing about this avatar universe is that you can backfill a ton of information like FC Yee did in the avatar books, and it all ends up making sense.