The full piezoelectric assembly has one metal electrode around its entire interior, but four different electrodes (as stripes) on its outside. The assembly thus acts as if it were made of four different segments. If we apply a positive voltage to the outside of the right segment, the table shows that it should widen radially (the field arrow runs from the blue segment of its Z towards the red segment). As it expands horizontally, it also gets shorter.
If we then bring the segments back together, you can see that this would cause the tube to bend to the right (towards our electrically shortened segment).
