This is part of the original German TUV requirements. The TUV is like the Department of Transportation (DOT) in the USA.
Cars registered in Germany are required to have at least one rear fog lamp. If only one lamp is fitted it must be mounted low (so it is lower than any fog, in order to be seen) and must be on the outboard (driver's) side. Porsches imported to the USA retain this German feature, which is actually a good thing.
So your car is fine and the fact that it only has one lamp is completely normal.
Personally, I like the little "secret" pull switch for this lamp.
In thinking about this, I wonder if Porsche switches the rear fog lamp side on right-hand drive cars? Silly question I suppose, but does anyone know?