I haven't read the paper in question, so it's possible they are talking about something completely different, but nonoriented may refer to the fact that (as in most powders and microcrystalline samples) there is no preferred orientation of the crystal planes of individual crystal grains with respect to the X-ray beam direction in the powder XRD experiment. If the crystals are preferentially oriented, you can get intensification of some peaks with respect to others, because those crystal planes can be more likely (compared to random orientation) to scatter X-rays to the detector.
Remember, unlike in single crystal XRD, power XRD looks at powders, and unless they are compressed or something you have almost by definition nonoriented crystal planes, because the crystal grains are oriented randomly in space. Think about, e.g., table salt. If you grind it up, the crystal planes are facing in lots of different direction with respect to the X-ray source, which is why you see scattering from all the possible crystal planes in the XRD pattern. Compare that to if you did the experiment on one single large perfect crystal, which would have a preferred orientation with respect to the X-ray source, so you would only see scattering from certain planes and no scattering from others.