Circular arc airfoil wing: why does the wing nose down twist due to camber? I am reading this paper: 
"Computational Investigation of Microscale Shrouded Rotor
Aerodynamics in Hover" Vinod K. Lakshminarayan, James D. Baeder ; JOURNAL OF THE AMERICAN HELICOPTER SOCIETY56, 042002 (2011).

In part "Rotor and Shroud Configuration" (page 2), the paper said: 


  " The blades used have a 2:1 taper starting at the 60% span location with the leading edge remaining straight and the trailing edge tapering toward the leading edge; this results in about 11 degrees nose down twist in this region due to the camber. The radius and the chord of the blade are 121 mm and 25 mm, respectively, making the aspect ratio equal to 4.84. A circular arc airfoil with 10% camber, 2% thickness, and leading edge sharpened from the 8% chord location is used."


I thought taper has nothing to do with angle of attack of airfoil section and the chord lines of every section lie in the same plane. How could the wing nose down due to camber?
I think it may be related to the geometric construction of the blade : 

Usually taper is made by scaling down airfoil at wingtip, which doesn't alter angle of attack at all. 



In this case the airfoil itself is cut along a line going from root trailing edge to tip mid-chord, which alters angle of attack with desired negative twist.