At best the boy from the story is to show that Uras has a tendency to show "compassion" for young males. There is nothing special about the well or the mask, which even the lore seems to throw in as an after thought.
Besides getting shot in the ganglions, something about young males is a weakness to Uras-Beherit. It could be as simple as them being the fastest vector which will cause the most suffering. Or as complicated as any theory could take us.
This weakness is ultimately where Uras-Beherit, or a piece of it, gets sealed away. Inside Ku'ur Sag.
In fact, it is highly likely the creature called "Emnu Dagan" is simply a bastardization of the story of the village Dagan. This story had spread far and wide and as time went on it became a thing of myth. A boogeyman waiting for careless children to leave their parent's side.
There was never an "original" Emnu Dagan. Mi'gel's mask gets pulled off and left behind. Also, the character he was pretending to be with the mask is never named aside from "fearsome birdman." I find it very unlikely that Uras-Beherit decided to keep that form, of a boy in a bird mask, just to terrorize the Locals. Uras' horrors are endless and such trivial things would go unnoticed, as they did when Da'ra removes the mask.
