Did Miller actually reverse that? or did they merely remand the case for more evidence?
The prosecutor then appealed that decision to the U.S. Supreme Court, and the USSC reversed the appellate court and remanded the case back to them to determine if the weapon bore a reasonable relationship to a militia.
The U.S. Supreme Court was saying, in effect, that the appellate court cannot say the NFA violated the second amendment unless they somehow determine that the weapon was a militia-type weapon.
This may have surprised the appellate court. They may have thought ALL weapons were protected by the second amendment, so they never even bothered to determine whether Miller's weapon was suitable for a militia.
Anyways, by this time Miller was dead and his partner pled guilty. That was the end of it.