The Pyramid is not hollow, it is filled in with the same stones as its perimeter. It could not have completed construction as there is no evidence the interior of the pyramid as an artificial lake.
I think the sense of the article is that the stones were lifted to the higher levels of the pyramid via ships that were movable water cranes.
As they hauled the stones upward, they would be dumped overboard to fill in the outer retaining walls. It’s just one of myriad theories that try to make sense of the construction since moving those huge stones by human effort without machinery of some kind seems impossible given the parameters of time, space, and volume.