Yes, that is exactly what they meant. "We don't know whether a sawed-off shotgun has a military utility, and nodboy showed us any evidence that it did, so we can't answer whether the second amendment protects the right to keep and bear a sawed off shotgun."
But the pertinent point is that the operating assumption in the ruling was that the Second Amendment PRESERVES the right of the people to Keep and Bear arms of military utility. The only real questions the court felt the need to answer are "what are arms" and "what constitutes military utility". The court simply stated that they did not have any evidence to rule on whether the sawed-off shotgun serves a military purpose.
So when people say that Miller enables the restriction of the weapons, they are totally wrong. I am especially dismayed at laywers (of which I am not one) who know damn well how to read this ruling, yet intentionally and dishonestly spin it to mean something else.
A lot of that going around in your profession. (And my daughter and son-in-law are lawyers, and they agree with that sentiment)