It doesnt have to be part of the challange it set legal precedent and such of the highest order. Any time anyone ever tries to argue the NFA there will be arguments citing Heller and Scalias ruling and him writing in black and white
So mentioning *Miller's holding that the sorts of weapons protected are those " in common use at the time" finds support in the historical tradition of prohibiting the carrying of dangerous and unusual weapons. Pp 54-56]* is Scalia giving he's seal of approval of the NFA? And yet the only dangerous and unusual weapon the SCOTUS has agreed with banning is a sawed-off shogun! (which Miller and his lawyer never show-up in Court for)
Scalia did not rule on the NFA! (Miller v US)
Scalia did not rule on concealed weapons prohibitions!
Scalia did not rule on longstanding prohibitions on the possession of firearms by felons and the mentally ill,
Scalia did not rule on laws forbidding the carrying of firearms in sensitive places such as schools and government buildings!
The Heller case did not fall under any of these.