  The man's breakdown is the result of his innability to hide behind his rational explanation for being happy that his son died happy. Even as he explains why he is not mourning the narrator describes him as bulging and as having inner violence. no matter what he says it is clear all is not well with him. As hard as he tries there is no way for him to pretend that his son's death does not phase him. When the lady finally asks him, not about the circumstance of the sons death or how he feels abut it, but wether his son is really dead or not, the man can no longer contain his feelings and it all comes out. It seems to me that the way the question is asked, if he is dead or not, forces the man to meet the facts head on and in that situation he can no longer hide from his emotions. 
