> A height map is representing voxel data without overhangs.

A height map can represent voxel data if the columns are integer heights, in the same way an integer can "represent" an infinite number of countable things. It's like saying the number 7 is "related" to a group of 7 ducks. The relationship is kind of meaningless.

But more importantly height maps can use also floating point heights in which case there's no reasonable mapping between the two. So your statement isn't generally true.