> the new fisheye lens consists of a single flat, millimeter-thin piece of glass covered on one side with tiny structures that precisely scatter incoming light to produce panoramic images.

With a thinness of a millimeter, I'd say that's flat. The "tiny structures" are in the form of a film, which further qualifies as flat.

> Their new metalens is a single transparent piece made from calcium fluoride with a thin film of lead telluride deposited on one side. The team then used lithographic techniques to carve a pattern of optical structures into the film.

> Each structure, or “meta-atom,” as the team refers to them, is shaped into one of several nanoscale geometries, such as a rectangular or a bone-shaped configuration, that refracts light in a specific way.

The 3µm-wide structures in TFA deviate <1µm from the surface, so it's even flatter than glass, and your objection sounds rather petty.