Why is the title ironic? Why does "The Guest" make a better title than "The Prisoner"?

The irony of the title is that the "guest" is not really a guest, but he is the prisoner of the French government.  He allegedly killed his cousin in the village, and the police are taking him to be tried for murder.

The original French title, "L'Hote," means both host and guest if translated into English.  The Prisoner would not make a good title because this story does not really concentrate as much on the Arab as a prisoner, but more emphasis is placed on Daru and his role as a host.