At the time Winston spies the lady who is a prole, he is looking down from his newly rented room above Mr Charrington's shop. The purpose of renting it is of course to enhance his surreptitious love affair with Julia. Winston is filled with dread at the implications of his own decision. Renting the room is a high risk action, but then it is also part of his fatalistic streak which sees him confide to Julia that he expects their whole world could unravel in as little as six months.
Winston's observation of the prole lady singing does not appear to radically alter his perception of the proles. We know that his opinion of them is not high based on his initial diary entry in the novel's exposition,
....nobody cares what the proles say typical prole reaction......(p.11)
At one time he had pinned his hopes on their large numbers to act as a force for change but this fades during the story. We can perhaps infer that as a result of listening to the lady sing well he has opened his eyes to the fact they they do have both talent and culture despite appearances (the lady in question is described as being a "monstrous woman, solid as a Norman pillar" p. 144). Winston notes with admiration that she has transformed the computer generated music offered by the state into a pleasant, singing tune. As her voice rings out through the neighbourhood, perhaps we could also infer that Winston has suddenly become fully cognizant of the more carefree attitude the proles have, most likely because of the relative lack of controls they live under.