This mechanic simply did not have the knowledge and experience to build an internal combustion engine
And exactly what proof do you have to be able to make this egregious claim?
Your cropped photo is of flight on the 17th Dec, and from the complete photo there is no evidence of any slope.
The brothers made a flight on the 14th December, but did not regard it as such because the launch ramp was set on a slope of 8° 50" at the foot of Kill Devil Hill. Photos below.
Federation Aeronautique Internationale (FAI) recognise the Wrights as making the first controlled, powered, sustained (from takeoff to landing) flight involving a heavier-than-air vehicle, using mechanically unassisted takeoff (thrust/lift created chiefly by onboard propulsion).