The book does not say, and Bentinho never presents proof: what he has is a resemblance. Ezequiel is the son of Bentinho and Capitu, born after years of waiting. As a small child he imitates the gestures of other people, among them Escobar's, such as the way of his feet and hands. In 1872, Capitu remarks at the table that the boy has a strange expression in his eyes, one she had seen only in a friend of her father's and in the late Escobar. From then on, Bentinho begins to see Escobar in his son's face.
The other side also has support in the text. Much earlier, the book shows that there are resemblances with no guilt at all: Gurgel finds Capitu similar to his late wife's portrait, with no kinship between the two. Bentinho recalls this in chapter CXL and, still, reads Ezequiel's features as proof. He himself tells that the boy copied everyone's gestures, from Cousin Justina to José Dias, and that José Dias, seeing the boy copy his gestures, said he seemed to be "myself, in miniature."
In the coffee cup scene, Bentinho says to the boy: "No, I am not your father." Years later, the adult Ezequiel appears at Engenho Novo, and the narrator sees in him "the very, the exact, the true Escobar," but confesses that at first it grieved him that the young man was not really his son. Ezequiel dies months later, of typhoid fever, on a study trip near Jerusalem. The question remains unanswered.