The step file is written by Solidworks. - You can open it with a text editor , all( professional-) programs write the exporter name in the start of the file.
Solid works (Still ?) uses Parasolid, so do NX and several other systems.
Parasolid is the "geometrical engine" in these systems , and the exact specifications of each little piece of the surface /face/ solid etc is "the same" in most of these.
- When you get data from a system that uses Parasolid , it is normally both "clean" and works as expected.
The pieces that are solids, such as the foundation in your file is both clean and "normal" , my guess is therefore that it was created in SW.
The intermediate arm, is a sheet body, the faces have several "unexpected" edges. ( Unexpected from my experience of how NX / Parasolids does things ), i would doubt that that was created in Parasolids ( i.e Solidworks), rather some "industrial design system" surface modeler. ( Rhino ?, Alias ?)
Regards,
Tomas