let's leave the wheel alone for a second, and imagine a stone in a notch at the top of a hill. Of you roll the stone a short distance in either direction it'll roll back into the notch. But if you roll it are enough it'll clear the top and roll down the hill instead. Keep that in mind when you think of bicycle wheels.

If a built wheel built wheel is flexed sideways a short ways, the spoke tension will pull it back into shape. However if flexed to the point of no return it'll "roll down the other side" and move to the bottom of the tension hill, which is the potato chip shape. You know that's true because the potato chip has slack spokes, whereas the flat wheel was tight.

Usually potato chips happen when newbies are flexing the rim to stress relieve or set the spokes and get carried away, but it can also happen with tension imbalance which has one area wanting to move right, and another move left. All that's needed is for this to be enough to bring the wheel past the point of no return. This is one reason that as a wheel approaches the tension limits that all changes me made in small increments and tension kept in balance through the process.