I'm glad somebody pointed this out! Meta materials and diffractive structures are not known for being low dispersion. This article mentions nothing about bandwidth. However, I think the writer assumes that the indented reader knows this already.

Also in the video you can see spatial ringing, which is highly indicative of coherent light (single wavelength, like in a laser.)

This is still a cool discovery and could definitely have a lot of important applications, but it's important to clarify what this is, and what it isn't.