It's interesting that the new alloy was not recognized by XRF. In the video it looked like they had a large set of standards from which to build an empirical model. I don't know how likely it is that Apple created their own alloy, but I have experience with XRF analysis and I know it's easy to make mistakes preparing a sample. It's possible the tungsten came from the sandpaper used to remove the anodization layer or it might have been part of the anodization layer. Another tricky detail when analyzing materials is how the different elements adhere to the surface. The X-rays only see the atoms at the surface. If sanding the alloy removes more of a softer metal or smears it over the surface covering the other elements you may get inaccurate results.