Then why include anything about affiliation with state-regulated militias in the question? Does the District of Columbia permit people who are affiliated with state-regulated militias to keep handguns and other firearms in their homes?
The citizens in question are not affiliated with a state-regulated militia. By making it clear that the issue does not involve a state-regulated militia, SCOTUS can avoid complications caused by the possibility of involving a state-regulated militia.
Post 104 captures my perspective... but your interpretation is understandable.