You are probably right, I didn't really pick aerofoils, it is beyond my level of knowledge.
It most certainly isn't zero drag, but at negative 2 degrees the additional drag as a result of the AoA is very small.
However, all that could be invalidated by the ground effect, again my knowledge of aerofoils in the ground effect is limited, the additional drag may be far more, the neutral lift point may not be -2 degrees, I can only go on my limited interpretation of the data which may be wrong.