All such incidents are very complicated in their nature, and in their bearings and relations.

They present many aspects which vary according to the point of view from which they are regarded.
Even grown people do not always see all the different aspects of an affair in respect to which they are called upon to act or to form an opinion, and children, perhaps, never; and in judging their conduct, we must always consider the aspect in which the action is presented to their minds.

In this case, William was thinking only of his aunt.

He wished to make her walk convenient and agreeable to her.

The boy disentangling his string on the sidewalk was to him, at that time, simply an obstacle in his aunt's way, and he dealt with it as such, sending the boy off as an act of kindness and attention to his aunt solely.