Is grounding the subpanel not required some times
That work is in metal conduit.  

You don't have any ground wires because the grounding function is being handled by the metal conduit pipes.  All my buildings have the same setup.   Nary a ground wire in sight.  

The dead giveaway of conduit is the non-"standard" wire colors; it isn't all black-white with the occasional red.   You will also note writing on the wires itself, not something you'll see with cable installations. 

Metal conduit is typically seen in commercial installations.  Note that large condo and apartment complexes, particularly high-rises, tend to be done to that standard.