Determining Finished Grade Plane Elevation Question!

Hello:

I am from Duluth, MN and am confused on a survey done to determine established grade plane for 3 townhome structures. The purpose of the survey was to show that the first floor was a basement to allow the structures to stay within the IRC building code. 

Attached are the survey and the builder's plans for the structures(they are identical). Can someone please explain how the grade plane was determined based upon the survey....Thank you!