When exporting a Normalized PDF or an IMP file (from FastImpose) that does not contain CMYK but only spotcolors, you will see CMYK appearing in the exported PDF (click the Info button).
See in the example above, it shows the info from a PDF exported from an IMP file. The original IMP file contains only the three Pantone inks. The same PDF when you open in Adobe® Acrobat®, in Print Production you might see the CMYK appearing.
Where does the CMYK come from?
The fact that the info of the PDF or opening the PDF in Adobe® Acrobat® (Print production) shows CMYK is related to PDF and the simulation profile.
To see the real inks of the PDF,
Check the info of the 'production file' (see screenshot below).