Meditation is a change in the “state of mind”. IMHO in meditation, sitting, standing or moving, when one experiences “non thinking” it is simply that the mind is not focused on internal dialogue. There are dimensions to what might be considered dialogue… In tai chi, the dialogue could be too much focus on what you are doing; enough so that you get absorbed in THAT WHICH YOU ARE DOING so much so that you are no longer experience that which you are doing. However, the objective is not to be totally a “cow” but to balance internal and external awareness; feel the changing of shapes that are guided by the knowledge of the Form’s physical, mental and spiritual principles, and breathe – let go into the moment.