a stack and whack pays no attention to the precise designs in the fabrics and you purposely mix different fabrics to make up the block after you stack then whack them into the designated number of pieces.
A one block wonder uses the pattern in the fabric in a very precise manner, and only one fabric per quilt (from the patterns I've seen). the look of the various "blocks" comes from the precise cutting that is done, and sections of the fabric are stacked up so that the same design is on each piece of fabric and is lined up exactly so that you get the kaleidescope design.
There are also kaleidescope quilts, which are similar to the OBWs.
Does that help?