I now believe I may be wrong. No cockpit windscreen could produce such a non-distorted reflection of a pilot's mask, as any sloped windshield would show a reflection of the dashboard. I apologise for my rudeness, as you are right in saying that I can't really know what I'm seeing.
With regard to the flat horizon. Both round earth and flat earth models predict a curved limit of sunlight. For round earth, the curvature is caused by the roundness of the earth, for flat earth it is caused by the roundness of the spotlight area where the sun shines. So the picture of a straight horizon does not prove a flat earth, but that your altitude is not great enough to be able to see the curvature in either model.