It was scaled down for pdf/print probably.
I took a quick look and although I am not familiar with autocad, there's a crude way to get it all to look right.
type SCALE to access the command
then select all objects
choose any point as a base point
put 1.5 as your scale and it should measure properly.
There's probably a much better, more appropriate way to do this.
I noticed that when I drew the measurement, I got the same result as you. Measuring between the 1.5" 1530 bolt spacing yielded 1" which tipped me off to the scale.