No, it is not a post hoc fallacy. The claim is not simply that death and dictators occurred after capitalism rose to dominance. The claim is that the economic incentive of infinite profit explains why these events happened. Specific wars were fought in to protect the interests of multinational corporations; the CIA installed dictators (e.g., South America, Africa), in order to stop the spread of socialism; there are slave laborers mining minerals in the Congo so that Tim Cook can make another billion.
If you want to get philosophical, perhaps we could agree that it is a category error to say that an economic system of commodity production caused death and dictators in the technical sense of causation. It would be better to say that these events find their ground or explanation in the incentives of capitalism. But I doubt most people care about this distinction.