Swarms that have just issued have been known to return on occasion, but usually because the queen did not go with them, often referred to as a false swarm. A swarm from August would not suddenly reappear to my knowlege. A swarm may take over a weak hive, that has happened, and I understand can be common with AHB swarms. My guess is your foragers are living longer and you are not seeing the attrition more common in the summer months so the population is increasing. Just a bit of speculation on my part but a strong hive going into winter is a good thing.
