IF you look carefully at the video, you can see the tiny bit of yarn used as an angle of attack gauge.
The Wrights were not just bicycle mechanics, they put a huge amount of scientific effort into their work. In fact, they discovered that lillienthal's equations for flight were in error.
Octave Chanute by the way was very impressed with the Wrights and even joined them one summer at Kitty Hawk with his own glider. Chanute wrote very positively about the Wrights and the US govt took notice.
OF COURSE Chanute was there and simplex1 is still pretty far away from Kitty Hawk,Nc