What makes the title, "Good Country People" ironic?

The title "Good Country People" becomes ironic in
Joy/Hulga's view of those around her and the events that occur within the story.
 Holding a PhD, Hulga views herself as superior to her mother and her neighbor.  She
regards their simple religious faith with condescension. They are blinded by their
naivete, Hulga thinks, as she scoffs their spiritual beliefs.  When a Bible salesman
comes to the house, Hulga believes that he is like her mother, another representative of
a "good country" person.  She stereotypes this man as being simple, innocent, and
unenlightened to the reality of the world.  A nihilist herself, Hulga wants to show him
the truth--that life is truly meaningless and absurd.  She plans to seduce him, to rob
him of his faith, and to make him see her way of viewing of the
world.

Ironically, Hulga has grossly misjudged this young
Bible salesman.  Instead of being "good country people," he, like Hulga, believes in
nothing as well.  He is immoral.  Instead of being seduced, he seduces Hulga, and robs
her of her artificial leg and leaves her stranded in the hayloft.    Hulga has
definitely met her match, and has been outwitted and outmatched by a pretender, one who
acts according to the very philosophy she professes.  In this way, the title becomes
highly ironic.