They're close - the OBW has you fussy-cutting patterns so you get the same repeat in several "blades" of fabric in order to make the block. The most similar to this is the kaleidescope block. you stack the fabrics so that you slash several layers at once, but they are very carefully placed.
The stack and whack (or stack and slash) is not fussy cut, and is not precise on where the cut is made. In this one you stack the fabrics then make the cuts according the the pattern you want to end up with - four patch, 9-patch, star, etc. Buggy Barn patterns are all stack and slash (that's my generic name for them, many quilters may challenge this.)