You're looking at something called a "neural radiance field" backed by a sparse, low resolution voxel grid and a dense high resolution triplane grid. That's a bit of a word soup, but you can think of it like a glowing fog rendered with ray marching.
The benchmark details are a bit complicated. Check out the technical paper's experiment section for the nitty gritty details.
Hahah I'm in formal methods, not graphics, so I'm picturing a literal green glowing fog. But what I'm gathering is polygons partitioned into cube chunks. This is of course not including the particulars of this impressive contribution, but I fear that's beyond my ken.
The benchmark details are a bit complicated. Check out the technical paper's experiment section for the nitty gritty details.