For one thing, by stating "this animal is definitely in the league with devils," the people who gather to see Esmeralda's trial are proving to be wholly superstitious. Recalling a witch-hunt ideology, the spectators are also, in a sense, proving to be a bit sexist. In patriarchal societies, men (and, even sometimes, women) are intimated by powerful and independent women and consequently dismiss their unwillingness to conform as mere witchcraft. This happens with Esmeralda when the jealous Fleur realizes Esmeralda to be a romantic threat; she witnesses Esmeralda's goat, Djali, perform a spectacular "spelling trick."
By labeling Esmeralda as a devil, these spectators are similarly dismissing her as inhuman; they are close-minded folks who are entirely unaccepting of other behaviors and lifestyles. They are also scandalous people who enjoy the provocation of a supernatural explanation for Esmeralda's behavior. She is certainly different, and the crowds that only hear rumors of her behavior are quick to dismiss it as simple witchcraft.