Me again...

Apparently it seems quite easy to reproduce.
Front and back curves were drawn using "Curves - control points"
Left curve was drawn with the same tool, right curve was mirrored.
Then I used the "Loft" command (closed).

Hope this helps....

Edit : I also noticed that when the control points were aligned vertically as you suggested, the "seam" line is slightly out of symmetry axis (see image).