Hello Fanman,
I'm no expert on the subject but as I understand it, the blade angle in degrees is the angle of the blade compared to a plane parallel to the blade root.
The angle of attack is the angle between the blade and the relative wind.
The relative wind is the trigonometric sum of the realwind and the headwind. The realwind hits the blades perpendicular to the plane of rotation, the one we measure with the anemometer where as the headwind is the "wind" that hits the leading edge of the blade as it's turning, so in other words the headwinds' direction is in plane of rotation. The realwind & relative wind are 90 degrees with respecto to one other.
As the blade speeds up or slows down so will the headwind, so your angle of attack is constantly changing with blade speed & wind speed.
Hope that helps...
Warrior