Who is the narrator, can she or he read minds, and, more importantly, can we trust her or him?
Third person limited
"Benito Cereno" is one long authorial trick based on point of view. The story is told from the perspective of Amaso Delano…and as you eventually find out, Amaso Delano is extremely unreliable. He has "a singularly undistrustful good-nature" (3.4)—and beyond that he's so racist he can't imagine black people taking any action on their own behalf. He can't see what's in front of him—and since you're restricted to his viewpoint, you can't see what's right in front of him either.
Melville could have told this story in first person and created a similar effect, perhaps. But putting it in third person limited makes it harder to realize you're missing something. In first person, you'd know you were seeing only what Delano saw. In third person limited, you feel like Delano's perspective is objective, true, and natural—it feels wider and more solid than it is. By using third person limited, Melville is kind of cheating; he's using those third person pronouns to throw you off the track, the better to surprise you with what you didn't know you didn't know at the end.