In my mind he didn't address the fundamental reason why the wing visibly oscillates while most other structures that you trust your life to like buildings, bridges, and cars do not. Airplanes are designed with a 1.5 factor of safety
A factor of safety is applied to a design after every load the structure will be subjected to is calculated, they multiply by 1.5 to be sure the structure will be safe. 1.5 may sound conservative but it is the smallest factor of safety someone normally encounters, spacecraft and fighter jets might use 1.2 while cars often use 3; buildings and bridges use 5. Airplanes are used much closer to the strength limit of their materials so we see them flexing.
Of course everything deflects under load - my strength of materials instructor illustrated this by analyzing how much an anvil compresses when a fly lands on it; answer: less than can be measured.
A factor of safety is applied to a design after every load the structure will be subjected to is calculated, they multiply by 1.5 to be sure the structure will be safe. 1.5 may sound conservative but it is the smallest factor of safety someone normally encounters, spacecraft and fighter jets might use 1.2 while cars often use 3; buildings and bridges use 5. Airplanes are used much closer to the strength limit of their materials so we see them flexing.
Of course everything deflects under load - my strength of materials instructor illustrated this by analyzing how much an anvil compresses when a fly lands on it; answer: less than can be measured.