Yes, you show a reasonable understanding of this. The others will have more to say, but I will just add that "MAT" files (abbreviation for "Materials") were originally an add-on to Poser 4. They were classified as "pose files" (filename.pz2), but they were used to apply materials settings and/or a texture file, often a jpeg, which was referred to by the MAT file, but not contained in it. Poser now includes a separate filetype (MT5) to apply materials settings, but it's still somewhat analogous to a MAT file.