QCAD does not produce 3D output. The second drawing is an isometric projection of the object. The lines and ellipse arcs in the second drawing are still flat (2D). They are merely the result of applying a formula (isometric projection) to the coordinates of the original lines and arcs.
Generally speaking, if you are only using two axis in any application (X,Y) and there is no third axis involved (Z), you are working in 2D space.