This article explains it.
https://www.theatlantic.com/politics/archive/2016/02/bushmaster-sandy-hook-liability/463245/
Those tactics, never tested before under PLCAA, dominate the allegations spelled out in the plaintiffs’ complaint. It quotes several advertisements from a catalog aimed at civilian gun buyers that is adorned with action photos of camouflage-clad soldiers and police in body armor. One reads, “Forces of opposition, bow down. You are single-handedly outnumbered.” Other images tout the rifle’s “military-proven performance” and call it “the ultimate combat weapons system.”
With that type of marketing, the Sandy Hook families claim, “The Bushmaster Defendants attract buyers by extolling the militaristic and assaultive qualities of their AR-15 rifles.” The complaint alleges that while the weapon is suitable for the military and for law enforcement—where it’s used for combat and limited police purposes—in civilian hands, the high-caliber, rapid-fire rifles are essentially killing machines.