The DXF file is a 100% geometrical translation of the NC file, which is created based on the DSTV specification.
In NC, the coordonates for the top/bottom/front/back faces are given based on the profile shape and the origin of the zero point. This zero point placement needs to have the same position for each face, and also on each face its positioned at the bottom-left corner. Due to this, the direction of the top/bottom faces will differ : one will be from the outside in, and the other one from the inside-out. I've attached a sample with a small model, and three pictures explaining how the faces are calculated.
The faces in NC can't be controlled dirrectly. Each beam will have a specific direction defined during creation, which is based on the internal coordonate system. This can't be modified by the user. The, the DsTV-NC criterias will be applied to the face assignation and to how the coordonates appear in the NC file. Then, the DXF just takes those coordonates and draws a contour, with no relation to how Advance Steel detailing works and creates top, bottom, front, back views.