There are key differences. In the case of the incubator story, cooked up I believe by Hill and Knowlton, the U.S. was looking for a reason to intervene and therefore manufactured one. In this case, no one wants to intervene in the Syrian conflict. The gas attack happened because of Assad's contempt for humanity and Russia's contempt for the norms of civilized international behaviour and the reasonable belief — based on their past use of chemical weapons — that no one will stop them.