Yes, but typically the different optical properties are strictly localized in space. Air here and water there. In this paper it's basically like you have a pool full of water with a light beam traversing halfway to the ground and then you instantly turn the air in the pool into water and the light goes, "oh hell no" and backs out of there
Isn’t that just like any material that light passes thru, which explains refraction?
Just sounds like they read Feynman’s QED book
Disclaimer: not a quantumelectrodynamacist