If you want to be pedantic, the paper made the leap it did because of differentiable rendering which necessarily needs a differentiable representation of primitives - so they use Gaussians. It’s entirely novel and set in a nascent field (neural rendering). Gaussians happen to be further representable as easily rasterized primitives. Though some considerable work was put into making this performant. Everyone who keeps saying this has been around since the 90s is missing the context of the very modern differentiable rendering literature.