At a glance it seems to me that it is simply an extension of the basic molecular orbital. On the extreme scale, eg metallic aluminium, you simply end up with a conduction band there are so many overlapping orbitals.
As you reduce the number of atoms down towards 1, the orbitals become better and better defined. That on some scale you end up with a configuration like that of an atom (whilst still having several nuclei) doesn't totally shock me.
