My apologies, you are correct only on the issue of which party appealed. (It has been about 10 years since I read the case, but that is still no excuse for getting that issue wrong.)
However, you are still wrong with respect to the real issues and my argument still stands, regardless of which party appealed.
Any of the lower courts or SCOTUS could have dealt with the standing issue. None of them did, reaching the merits of the arguments from both sides.
Therefore Miller stands on a procedural posture for the fact that the second amendment protects an individual right.
Can you understand that or will you choose to ignore that fact?
Nope. The U.S. Supreme Court could have ruled that the tax was unconstitutional because it was an infringement on the right to keep and bear a shotgun -- without saying who would do the keeping and bearing.
Taxes on products have been ruled unconstitutional without the court identifying who is affected.