As they state at the bottom, they are referring specifically to geodesics when they mean straight line. They then rule out the due east curve, despite stating y

As they state at the bottom, they are referring specifically to geodesics when they mean straight line. They then rule out the due east curve, despite stating you must travel due east. They claim this is because to do so would make the line no longer straight, but this claim is utterly nonsensical in the context of three dimensional geometries. This is a puzzle born of a misunderstanding of three dimensional Euclidean geometry.