I believe the point is that we understand the birds' flight better applying the principles we learnt designing and flying airplanes. Similarly, we can learn more about human brain by applying things we learn from building the ANN back to the study of humans (anthropology in general, maybe neuroscience and psychology )

Concepts from the mechanics of flight (e.g. lift and drag) have helped ornithologists understand birds better. Birds themselves did not learn much.

He didn't say it fed back into birds, but into the study of birds.

Knowledge learned from airplane propeller development, as well as from jet plane wing aerodynamics, has had a great impact on the design of wind turbine blades, which are now affecting the evolution of birds.