Hello. You did not indicate which scene and which play you are referring to. However, Arthur Miller's plays have many scenes of situational irony and the author uses this type of irony to surprise the audience, because it allows a totally unexpected situation to happen, something totally different from what the audience expected.
An example of this can be seen in "the crucible" when Rev. Hale tests John's religiosity by asking him to recite the 10 commandments and proves innocence in his accusations. Since John is a very eloquent and Christian man, the public is sure that he will have an easy time reciting. He really has it at the beginning, but he starts, but he can't recite the 10 commandments and he recites just 9, surprising the audience.
