It would perhaps be to much to ask that Roberts be more knowledgeable here. He has only been a judge for about two years, I think. Its possible he has never had a case involving the Second Amendment.
On the other hand, there are only ten articles in the Bill of Rights. One might think that he would have some rather informed opinions if he thought that one of them had been seriously infringed for more than seventy years.
Roberts' statement about Miller strikes me as erroneous. If there had been a "collective rights" issue then one might have thought that the Supreme Court would have refused cert on the basis that Miller had no standing to bring the case.
From US vs. Miller:
The signification attributed to the term Militia appears from the debates in the Convention, the history and legislation of Colonies and States, and the writings of approved commentators. These show plainly enough that the Militia comprised all males physically capable of acting in concert for the common defense. A body of citizens enrolled for military discipline. And further, that ordinarily when called for service these men were expected to appear bearing arms supplied by themselves and of the kind in common use at the time."
It appears to me that there is no "collective rights" issue at all. "Every male capable physically capable of acting in concert for the common defense" might be termed a "collective" but each such individual was expected to arm himself and the Second Amendment prohibited infringement or his right to do so.
Roberts is perfectly knowledgeable here. He correctly notes that:
1. The "collective rights" versus "individual rights" argument was raised, and
2. The court sidestepped this issue, ruling instead on the question of whether a sawed-off shotgun was a type of weapon that fell within the scope of the Second Amendment. (As others have noted, they got this question wrong because Miller's side did not present any evidence, presumably because Miller had shuffled off this mortal coil before the case reached the Supreme Court.)
From this, we learn that Roberts understands that gun-control arguments asserting that "Miller is a precedent establishing the 'collective right' doctrine" are worthless jaw-flapping.
I look to Tench Coxe as the person who wrote the best interpretation on the subject,