So what? So is the M79 and the M249 SAW. What the hell do they have to do with a sawed-off shotgun?
The AA-12 is a bullpup design used for building clear. The "Master Key' is used as an underslung 12ga attachment for the M-16 platform. Both are illegal for civilians to own despite there being a demonstrated "militia purpose" and even a "sporting purpose" for 3-gun matches.
Basically, your statement of "it's not a militia-type weapon" was your typical dodge on the issue.
Any weapon is a militia weapon. This ruling points out that the Right to Keep and Bear Arms isn't limited to a militia purpose nor a sporting one.
You still haven't read the whole thing... have you...
They're functionally equivalent to what Miller was in trouble for having, and which SCOTUS ostensibly couldn't see an obvious military use for.
I'd go so far as to say: in observing that the defense didn't show up to court, and recognizing the serious relevance of the case, SCOTUS was looking for a way to make the case go away without making a binding ruling - as to do so would be unfair to both sides. Better to a relevant yet easily-answered question which sends the case back thru the system, allowing Miller to pursue his case (if he ever showed up (difficult, being dead)). It's not unusual for courts to seek any way to weasel out of making a ruling (even in Parker, only one plaintiff was granted a full ruling).