Yeah, "when" was not the corect word. See my post #174.
You are correct -- Miller only referenced the type of arms protected. Subsequent lower courts have addressed the "who" is protected.
Fortunately, or not as the case may be, the Supreme Court is not bound by lower court decisions. Even other lower courts are not bound by them, although they may be influenced in their own thinking by them. That's true even if there is no disagreement between the circuits.