PDF pages are physical objects with dimensions in points (72ths of an inch) - there is no concept of a "1:1 pixel scale" for a page and you can have many objects on a single page with different dpis (plus a mix of raster and vector objects).
"100% scale" in Acrobat and Reader is a physical scale representation using the OS definition of the pixels per inch on the monitor. As hardly anyone has a monitor with a physical scale correctly set, it's usually just a vague approximation.
So, it is not possible to find out the pixel dimensions of raster images in a pdf document? In fact I don't know if access to all images is even possible. As I said, I tried export and it didn't exported all images that I can see.
In Acrobat Pro, choose Tools > Print Production > Preflight.
Select any check (it doesn't matter) and press the "Analyze" button - not the "Fix" button.
In the results tree which then appears, open "Overview" and "Images" to see a list of every raster object in the file, with details of size, color space etc. If a graphic on the page isn't in that list it means it's a vector object.
Alternately, open the PDF file using Adobe Illustrator.