Is there any hint in the story that the fat man was not as sure of his argument as he claims to be?

One of the reasons that Pirandello's story is so effective
is that it rests upon the fat man's certainty.  He enters the car and commands the
center of attention.  He gives a spirited discussion as to why he is glad his son chose
the path he did.  There is little weakness in his argument.  He delivers it with so much
bluster and so much zeal that it is something that cannot even be questioned.  There is
no hesitation or reticence in what he is saying. His entry and his declaration are seen
as antidotes to the ambiguity that the other passengers are immersed in prior to his
entry.  At the same time, Pirandello makes it clear that the certainty of the fat man is
precisely what compels the bundled up woman to speak.  She does not say anything.  In
fact, Pirandello describes her as "waking up."  She does this because she senses the fat
man's certainty and his sense of absolutist faith in what he is saying and in what he
believes about his child's death.  She finds encouragement from him because of his own
sense of confidence.  This would clearly suggest that the fat man was certain of what he
was saying. He is only disarmed when the woman speaks, asking her fatal question that
reveals his own certainty as nothing more than illusion.