The point is that there is a simple and fundamental flaw in many of the papers studying cognitive dissonance, e.g. the Santos m&m paper. The significance of this flaw is that the m&m paper (and others like it) has no interpretable conclusion -- the results could indicate cognitive dissonance or they could indicate an initial asymmetry in the monkey's preferences. The design of the experiment precludes any clean interpretation. Indeed, if the m&m article was submitted for publication now it would not be accepted because no conclusion can be drawn.

Even if there is a recent well designed experiment showing cognitive dissonance does exist, it is still important and worthwhile for Chen to point out the design flaw in these earlier experiments.