The storage media was a floppy disk (literally) for all three sizes The casing was either flexible but not really floppy (for the 8- and 5.25-inch versions) or rigid (for the 3.5-inch version) and square (not a disk) for all three versions.

So the only thing that "floppy disk" ever made sense for, even for the 8" ones, is the storage media inside the casing, not the casing.