This is actually not "our" or "my" measuring tool... You area posting on the Adobe Acrobat User Community", which means that we are all users of Adobe's PDF technology, just like you. This is not a mechanism to directly talk to Adobe.
There is no documentation I am aware of that talks about how accurate (or not) the measurement tool is. One problem is that when you drag the tool, you may not hit exactly the line or the corner, or in case of rectangles, the original rectangle, that will definitely add to the inaccuracy vs. what you have in AutoCAD. But, what's probably more important is that when you convert from AutoCAD to PDF, you are dealing with rounding errors. Chances are that the two systems are using different number types for their calculation, and when you convert from one to the other, you are introducing inaccuracies.
Then you have the issue of line width: Chances are that AutoCAD measures from the middle of a line. Depending on the line width, you may end up measuring slightly off the center.
These issues, added with how accurate or inaccurate the reviewer drags out the measuring tool will very likely result in results that are slightly off.
Again, you may not be able to find anything official from Adobe, but you should be able to explain why the numbers are close, but not identical.