You're right, so they could build in a series of proximity sensors in different axes and have the ball sense the presence of the wand but that gets complicated really quickly and we're talking to a beginner.
Much simpler to have a hidden button (even perhaps one in a separate box to inhibit/allow movement so the audience could participate) and a couple of tilt sensors in a wand activating different inputs on the HT12 already shown, as for predicting the direction, yes, the ball could be marked in many ways which aren't obviously direction markings, many children's play balls are already printed with pictures or patterns for instance, or they could just watch which way the ball rolls and steer accordingly.