When the magnet is bashed it will not always be located by a wall, but when it is by a wall it will cause eddy currents which cause heat in the aluminum. This is not meant to be a practical system that produces any energy, as it takes energy to move the bumper cars. It is a thought experiment to demonstrate that random motion can produce random eddy currents, slowing cars (particles) down over time due to continual drag in the system when the magnet is near an (aluminum or copper) wall. If the cars start out with an initial speed and have no more added, they will eventually all come to a stop after time. The aluminum must be insulated to keep heat inside the metal and isolated from the cars (particles).
The drivers of the bumper cars may be drunk and chaotic and move completely randomly. Despite the motion being random, heat is extracted. Logically it should follow that room temperature fluids offer similar kinetic energy at the microscopic or nanoscopic scale.
Can internal energy from fluids be drained without a cold sink, breaking the 2nd law of thermodynamics? Do eddy currents allow the second law to be violated by separating hot from cold? This would have to be tested with nano magnets undergoing brownian motion in a nano institution lab that could produce such a device. One possible falsification is that the eddy currents themselves produce a moving magnetic field, or Johnson/Nyquist noise plays a role and heat gets transferred back into the microscopic realm. However this would have to be tested as the magnetic field produced by the eddy currents or Johnson/Nyquist noise may not be equal to the amount that the magnet moves, and there may be a non-equilibrium condition to be exploited. An example of what may happen: the magnetic field in a nano sized device due to eddy currents or Johnson noise may be randomized in such a way that it never reaches back into the fluid fully, or the field spreads out enough not to affect the magnet (backfiring). This would need to be tested by nano institutions to verify that nanoscopic devices cannot exploit eddy currents to sink heat.