TLDR They use a neural net to process an image to find a similar known 3D model to the object in the image as well as parameters for how to deform that model to be like the object in the image, and also then perform a linear combination of some related meshes (this is a follow up to their prior work "Compact Model Representation for 3D Reconstruction"). Pretty exciting work, but still far from being able to robustly do Image2Mesh. I happen to have worked on something quite similar, if any of you are curious: https://deformnet-site.github.io/DeformNet-website/