Here is an excerpt from his blog:

"""""""they were transformed into a surface using the Loft command. It was necessary to use the Loft option Loose to generate a relaxed surface. One of the most tricky parts of the whole modelling process however was a clean definition of the guide curves as the resulting surface, as kinks and unequal control points had to be avoided in the guide curves. Lofting the curves together it is very recommendable to use the same number of control points in the guide curves. In order to achieve that the Rebuild command was used to equally spread and define the number of the control points along the guide curves. If the car body surface is not clean, this will generate many problems in the further modelling steps, as cut out surfaces and other constructions will tightly rely on the main car body surface."""""""""

The "half of the body" is doen the center of your red curves. Lools like you ate trying to do a "top half, bottom half", when it should be a left/right split.