And if you are tense with a raised wrist (I am not), perhaps you need to work a little more on some relaxation techniques.
To explain what he was doing, if you place your arm and hand on a flat surface, such as a desk, (in a similar position to how it would be if you are playing) and relax the mechanism completely. You can then push the fingers and hand down using the 'wrist snap' motion. It results in forearm lifting and the wrist position being high off the desk.