The beauty is that you can make the mental gymnastics to make it work both ways.

If they are opposite, the magnet attracts the car which moves the magnet away creating infinite motion

If they are the same, the magnet is repelled by the car, moving it away, moving the car forward creating infinite motion

You can even do mental tricks to make the contraption go backwards: Opposites: car attacks magnet which moves the car backwards Same: magnet reppels the car which moves the contraption backwards