1) The prepositions contribute a narrative feel to the anecdote, distancing Orwell from the events and shifting any potential judgemental views onto his friend, the main character, and not him, the narrator.
2) Orwell’s tone in the extract comes across, in my eyes, as informal. His use of a more generalised phrase in the opening sentence (‘a couple’) makes it seem less set-in-stone and less precise, creating a more informal manner of writing. The succession of embedded clauses inject extra, more personal, information and contribute to the general tone.
React!