In "The Storyteller" by Saki, why is it ironic that the children favored a story told by a bachelor?

It is ironic precisely because of the fact that a
bachelor, because of his status as an unmarried man without children, should not know
how to tell a story that could appeal to the imagination of children, especially when
compared with the aunt, who, because of her status as being an aunt and the time spent
with her charges, should, in theory at least, know how to tell a story that the children
would like.

Of course, the irony lies in the way that the
bachelor tells a very nontraditional children's tale, which, in the words of the aunt,
"undermined the effect of years of careful teaching." The way in which the bachelor's
tale and the kind of values that it presents managed to capture the attention of the
children, in spite of the bigger moral "tragedy" as the aunt saw it, is another reason
for the massive irony of this excellent short story. What is moral and improving is not
always what is interesting.