Lighting in video games encompasses a lot of things these days. I'm not a graphic designer but, to my untrained eye, it looks like this tech is pushing hard on things like subsurface scattering to make materials appear more realistic. It doesn't appear to be changing the actual polygons. This picture further down seems like a more realistic example of what it would end up looking like when the technology is complete. I think they picked that particular first image as an example BECAUSE it's such a stark change.

This isn't applying a filter, it's ~~applying~~ running the image through a transformer network trained on advanced lighting methods like subsurface scattering to make materials more lifelike. It seems to change artistic intent quite a lot on these existing games, but frankly I'm excited to see what creators do with a game designed from the ground up to utilize AI-enhanced lighting. The DF video also states that this is an early preview (hence the dual 5090s) that is expected to change over time.