As I understand it, the OBW uses all the fabric. You stack them and cut them but the fabric determines what your Kaleidoscope looks like. The octogons(?) are sewn together touching each other, no background or sashing.
Stack and whack is where you fussy cut your fabric to create Kaleidoscopes of your choosing. These usually have dark, solid fabric corners added to create a square block and sometimes have sashing added between the blocks. The Kaleidoscopes are framed and do not touch each other.
I think, and emphasize" think", Bethany Reynolds coined the phrase "Stack and Whack" and Maxine Rosenthal coined the "One Block Wonder".
Creating the blocks are basically the same technique, you just sew them together differently.
Always in a Texas state of mind.