Hi Cuorematto,
Bi, Tri & Aniso refer to the type of texture filtering: Bilinear, Trilinear & Anisotropic. The different methods of texture filtering have difference costs so it is possible for a shader to be ALU bound when using bilinear filtering and texture fetch bound when using anisotropic filtering.
You can find further details on all statistics calculated by GSA in the release notes.
Cheers,
Seth.