Because this narration is restricted to one who left his house without the intention of travel, then the travelling continued with him until he became a traveller without intention; it became binding upon him to perform fully (the prayers), even if the distance reached that which, had he intended it, shortening (the prayers) would have been obligatory upon him therein. It only became binding upon him to perform fully because he had not intended a journey of the amount in which shortening becomes obligatory upon him. And what supports this interpretation is what he narrated (in the following hadith):
Commentary #10