This is a vague statement. Are you suggesting each column can can have multiple layers of terrain, air, terrain? IIUC, the article disputes this:

> Such maps limit the terrain to “one height per position on the map” - Complex geometries such as buildings or trees are not possible to represent.

FWIW I'm working on a voxel sandcastle game. People usually seem particularly surprised by this style because they're so used to such games being rendered by height maps which don't allow tunnels or arches or overhangs.