Also seem like it ray traced global illumination and not radiance cascade.
So they just render the light by ray casting into the scene either from the light source or the camera, which I think is what they did here since there are some part of the video showcased from their lighting system shows the specular highlight flickering and based on the amounts of travel hit/indirect, detect, reflect place a point light at that location and apply properties on the info collected from the environment through all the ray traveled.
Here are some resources that done this:
Many's Ray Tracer 2.1! [GI and MORE!], [DEPRECATED] Ray-Traced Global Illumination Plugin | Make your lighting look Incredible!.