I think it is just a joke. If you wanted to be able to turn it, you'd have to switch to just two wheels, diametrically opposite at the midpoint of the mower (unless you wanted to set up a mechanism to lift up the front wheels whenever you wanted to turn). Also it has standard single-speed pushbike gearing, with about a 3:1 step up in gearing between sprockets, and an additional 1.3:1 step up between the pedal swing radius and the back wheel swing radius. There is no way you could pedal hard enough to move it through actual cuttable grass, even on the flat.
