Jack London included the detail because "it is a part of the exposition that introduces Sol-leks' characteristics."
Explanation:
The detail is an exposition that introduces Sol-leks characteristics.
Exposition means showing or narrating what happens at the start of the story. Generally, it talked about the background of a milieu, or a character, which in this scenario is Sol-leks.
The details illustrate what kind of dog Sol-leks is, what are his likes and dislikes. Because these characteristics or details will play a crucial role as the story goes.
As the story goes, the position of Buck and Sol-leks will be reversed. Sol-leks being afraid of Buck because of a brute strength he displayed later on.
Dante also uses similes, comparisons of one thing to another using "like" or "as," most notably in his remarkable description of the souls of the condemned moving onto Charon’s boat
