Not really topology, it's more like group theory, and representations.
Ordinary convnets are a way of building in translational symmetry, which is the group R^2 (in the plane). The work being described extends this to larger symmetry groups, such as rotations of a molecule in 3D (which is SO(3)).
For either of these, you can work in Fourier space instead of real space, where convolutions become products. For ordinary convnets means ordinary FFT, but nobody does that as translating to neighbouring pixels is simple enough. Rotations aren't so simple, and so working in Fourier space can be an efficient way to do things. And the connection to physics is really just that the representation theory of SO(3) is a bread-and-butter exercise there, the basis of atomic theory.
Ordinary convnets are a way of building in translational symmetry, which is the group R^2 (in the plane). The work being described extends this to larger symmetry groups, such as rotations of a molecule in 3D (which is SO(3)).
For either of these, you can work in Fourier space instead of real space, where convolutions become products. For ordinary convnets means ordinary FFT, but nobody does that as translating to neighbouring pixels is simple enough. Rotations aren't so simple, and so working in Fourier space can be an efficient way to do things. And the connection to physics is really just that the representation theory of SO(3) is a bread-and-butter exercise there, the basis of atomic theory.