nice shot! Well, paper planes are not as advanced as comercial ones, obviously, and their wings are flat, and they work both the plane is upside down or it isn't. And if it's not because the shape of their wings, why can they "surf" the air and make loopings, and if instead of making a plane, i make a ball paper, it cannot do it?
PS: No, it's not my first language, in other posts i apologyze for my poor english. I'm curious, how did you notice that?