Explorer,
The most obvious error is having the blade slow down over the 2X to "SAW" it in a near perfect cut along the marked cut off line then dropping to and sticking in the ground without rolling along, which means the blade wasn't spinning when it stuck.
Teeth forward, means that if the thrower were able to control spin by using topspin the blades forward momentum combined with the direction of the teeth would have forced the blade to walk over the 2X before flying off at an equal tangent instead of dropping to the ground.
If he were able to apply back spin the blade would have jumped up when it hit the 2X, like a tennis ball.
Turning the blade around would have teeth throwing saw dust forward in stead of back.
All actions have and equal and opposite reaction related to inertia, angle of approach and rebound, (ask any pool player or sharp shooter). The blade and the 2X had to be in fixed positions to saw the 2X and throw saw dust.
