Being close to failure isn't a requirement for visibly bending. For example, see wire rope or cloth. Anything very long and thin can flex a long way without much strain on any individual part of it.

Low FoS yes, but even if you doubled it to 3, you'd still see the wing tip moving - only half as much.

Truck trailers are also very soft in torsion. See an empty one go over a big bump and it'll visibly twist. Not close to failure, just not very stiff.