I never liked that story.
Of all the fables, that was the only one that 'bothered' me as a child. I didn't know how to voice the reason it bothered me because at that age I lacked the rhetorical and logical thinking to distill and communicate it, but I can identify and describe it now.
The boy still should have been believed; It's illogical to dismiss the warnings of a disastrous scenario as "meh, probably a lie" (look at climate change today!!).
In the case of the villagers, it would have been better to be duped again then lose a flock of sheep. Plus where was the boy's punishment for his trick on the first or second iteration?
The Villagers did not do justice to the boy's moral education by letting him off "scott free" with such an irresponsible prank. They, as elders are thus equally as responsible for the loss of the flock as the boy is, if not more so.
For A; not educating the boy on the severity of his wrong doing IMMEDIATELY on the first instance of his trick, AND enforcing it more severely the second time or confiscating the flock and giving it to a more responsible Shepard.
and B; for choosing the risk of losing an entire flock of sheep, over the risk of "slightly wounding their collective egos and wasting a trip so the boy can laugh at them". What are they, a bunch of 12 year olds!? They put 'not being laughed at by a young person' ahead of 'losing a critical resource to the entire village'.
How irresponsibly stupid, lazy and vain of them.
A truer moral ending to that fable would be, the villagers DID respond to the boy (because that is the only non-idiotic option), and indeed saved the flock.
Then on a subsequent "false alarm" raised by the boy for his own amusement, the villagers again respond but find they've been tricked; They immediately confiscate his flock and entrust it to a more responsible Shepard and the boy is sentenced to tougher labour, performed under supervision.
The boy is now sheep-less and understands the consequences of being a little shithead, without it costing the village a very vital and important resource.
In the fable as it stands, the villagers were more at fault then the boy.