It is a 1 rail sweep with a scaling rail.

>>How would you have done this without the scaling rail? I guess maybe NetworkSrf with 4 curves in each direction, or it looks like 2 rail sweep with 2 wavy rails.
<<

The last method is how I'd do it in Rhino.
It would be a 2 rail sweep with the same cross section profile as I used in MoI.
a circle for the finger hole and a wavy curve offset outside
of it -which would be more complicated to draw than the scaling rail curve.

The result of this kind of sweep in Rhino is somewhat unpredictable.
The waviness is an effect of the sweep, rather than a predetermined shape that
you can easily control,

-Jesse