The claim is inaccurate and was a common myth of the French national narrative, even before the revolution. The wildly held belief went that since France was the land of the Francs (freemen), there were no slaves in France. Nonetheless, the French Empire had implanted slave societies in Martinique, Guadeloupe, Louisiana or Saint-Domingue, and the First colonial Empire also relied on the enslavement of Native Americans. Orientalism was trending since at least Montesquieu (by the way the theory of climates he was defending would serve as a template for racial "science"), and it would result in the terrible exactions of Napoleon's army in Egypt and Palestine not even a decade after 1791. All these phenomenons relied on a racial system that divided European races from African or "Oriental" ones, so saying that "racial prejudice was foreign to France" is blatantly false.