Converting polygon data on the fly would be pointless as that in itself couldn't really be any faster or more detailed than existing polygon scanline rasterization techniques, and you would still need to store and index all that data before you could search it. The conversion algorithm would have to be magic to be able to take a mesh and turn it into a point cloud with more detail than the mesh, or to make the conversion.

Also the description in the video was that the point cloud data is what is being stored right down to the level of what would ship with the game. That's what all the stuff about scanning in rocks was about. The rock exists as point cloud data, not a mesh that is converted to a point cloud.