Note that this is just one recent work in a well established research problem that has been worked on for decades. The interesting bit here is that they appear to achieve state of the art results by doing something simpler than other approaches - instead of fitting a well thought out generic morphable face model, they use a pretty standard deep learning model to map a 2d image to a discretized 3d model of the face (voxels). Intuitively this feels a bit off, since outputting a discretized 3d model instead of fitting a continuous model has inherent resolution limitations, but the benchmark results are pretty impressive.