
Look at the lower Left. At the very corner, the line is practically touching the land, and then it drops lower as it moves toward the center of the line-length. You can see the black between the line and the earth. Toward the center there's still some black. Then as you move toward the upper right, the land mass or geography gets higher and comes closer to the line, and then in the far upper corner it slips slightly down.
So the lower left tip actually moves upward and touches the line, and it's only again close to the upper right where the land touches the line. It just happens to dip back down a tad at the upper right corner, but no more so than it did in the center. That undulation of geography is what the globetard who made the graphic above is claiming to be "curvature.