Its hard to say exactly because the OP doesn't go into the runtime mesh used but my guess is its quite different form Nanite.
Nanite assumes high poly authoring of objects and works to stream in simplified chunks such that the rendered triangles are not less than a pixel wide. Displacement maps are a bit redundant because geometry can be naturally very detailed, there's no reason to use a texture map for it. (There is a case for Landscapes but that's a unique case)
This seems to be using a displacement and a low poly mesh to generate high poly but 'voxelized' geo on load.
Nanite assumes high poly authoring of objects and works to stream in simplified chunks such that the rendered triangles are not less than a pixel wide. Displacement maps are a bit redundant because geometry can be naturally very detailed, there's no reason to use a texture map for it. (There is a case for Landscapes but that's a unique case)
This seems to be using a displacement and a low poly mesh to generate high poly but 'voxelized' geo on load.