Oh, I see what you mean now. I'm not used to seeing notations like that arrow so I totally missed it at first.

Based on the angle you measured and the note on the plans that say it's 2 degrees down then I'd have to agree with the wing beeing at zero. But zero to what? SInce there's no reference line shown on the plan and given the measurement agrees with the notation I'd suggest that the manufacturer set the thrust line to the wing's chord line. So the wing's chord line is the reference line. At least the absence of any reference line on the plan plus the fact that your lines also show a 2 degree angle strongly suggests this.