The message is as explicit as you can get: you cannot accurately unroll doubly curved surfaces. Look at the video again and notice that the polyhedron is made up of flat faces. Think of a box and how you would draw that out on paper to then cut it and fold it into a box. Again, this example box has flat faces. When you start to have curved faces, you begin to run into inaccuracy. Single curved faces, like a watch band, will unroll accurately since most likely this will be a ruled surface. In general, to be unrolled accurately, the faces of the object should be Developable Surfaces. Other commands such as _squish or _smash might attempt to flatten the object. _squish in particular has some options (Decorate=Yes) which will show you how the object has been warped on its way to getting flattened.