Your single layer theory has been thoroughly vetted and debunked by experts around the world, including Adobe. Deal with it.
Name them and show their work. Because this is not the case, merely wishful thinking on your part.
"PDF files can contain layered content if they are created from layered documents by using applications such as Adobe InDesign. As a result, a single page of the PDF file can contain different layers with different content."
-- Adobe
http://helpx.adobe.com/acrobat/kb/printing-complex-pdfs-acrobat.html
Nuff said.
The PDF in question was not created from a layered document, but from a scan, which by definition is not a layered document, a scan can only produce a single flat image with no layers, objects or anything else. It is subsequent software processing which may produce one or more layers.
Adobe Indesign was not involved in the process AFAIK, unless you can prove otherwise.
Your precious Adobe quote is not applicable. A scanned document cannot have anything other than asimgle bitmap image. What is done with that image afterwards, even down to the simple choice as to what format to save as, will drasticly affect the creation of other structures.
This has been explained to you in enormous detail within this thread. Subject matter experts have explained it to you repeatedly, yet you stubbornly insist that YOU are right, in the face of the evidence, nay, the reality.
Really, Bob, you should concede gracefully, because if you continue along this vein(vain?) line, you will continue to be buried by the expertise you failed to consider might be present on this forum.