Because an EnsembleArray can be treated similarly to an Ensemble, this documentation is just intended to make it clear that they are distinct. When an Ensemble is 2 dimensional you can calculate a nonlinear function (e.g., x[0] * x[1]) of the represented values because the neurons are sensitive to both. If you have a 2D EnsembleArray with 2 Ensembles each representing 1 dimension independently there are no neurons that are sensitive to both x[0] and x[1] and so it’s not possible to decode a nonlinear function (such as x[0] * x[1]).