It would be interesting to see a screen shot of the element and tool you’re using along with the readout of the measurement because, for me, using Illustrator’s direct-selection tool and Acrobat’s preflight analyzer has always shown the expected size of raster elements.
So far as file “bloat,” how are you gauging this?
The overall Illustrator canvas size you’re seeing is the previous and common limit of Adobe PDF maximum dimensions using Illustrator. It’s always been there but fully revealed when Illustrator introduced their multiple art boards feature many years ago. Rather recently though, Adobe answered user requests to increase the size dimensions limit. So, now available, is their “large-scale” canvas 100 X larger than before.