Looks like the author tried to double-power the motor with both the spacecraft motor driver and through the breakout box that MITMs the driver and the motor. In such event, the free-wheeling diode in the driver will allow reverse current to be fed back to the driver's power supply up to certain amounts. This will absorb back-EMF, or energy from "regen" from the motor.
I'm suspecting the breakout wasn't literally sitting between the driver and the motor, but rather all internal connections are broken out to the box for testing; and likely the author's mistake was to not mess with the spacecraft to temporarily disconnect the driver.
But I'm not sure if I'd "just" made the right call and done so nonchalantly on a Mars rover to launch in few weeks.
I'm suspecting the breakout wasn't literally sitting between the driver and the motor, but rather all internal connections are broken out to the box for testing; and likely the author's mistake was to not mess with the spacecraft to temporarily disconnect the driver.
But I'm not sure if I'd "just" made the right call and done so nonchalantly on a Mars rover to launch in few weeks.