I think that, in this case, your load resistances are too low.
Try increasing the output load resistance (gradually) and see where the SMPS starts switching, giving you the negative output you expect.
I believe this circuit is only for providing a negative "rail" (or potential) of little current capability: something you might use to assure that, for instance, and OpAmp comparator circuit output goes all the way to zero volts (or less) when appropriate.
On that note, there are simpler circuits for that purpose...