The page shows, near the bottom, how the main output is gaussian splats, but it can also generate triangular meshes (visual mesh + collider).

However, to my eye, the triangular meshes shown look pretty low quality compared to the splat: compare the triangulated books on the shelves, and the wooden chair by the door, as well as weird hole-like defects in the blanket by the fireplace.

It's also not clear if it's generating one mesh for the entire world, it looks like it is - that would make interactability and optimisation more difficult (no frustrum culling etc, though you could feasibly chop the mesh up into smaller pieces I suppose).