I guess they mean the actual storage was illegal which it clearly was, not the fireworks themselves...I did catch a glimpse of some Brothers products in that massive stash Guessing they were gonna be used for July 4th too
The US laws on fireworks can be quite confusing, with federal, state and sometimes county regulations with some massive variations across all the States. There are places where consumers can buy some shells and other places where "safe and sane*" (ie sparklers and fountains) applies and other places where no fireworks are permitted. Hawaii is a NO Fireworks area yet each year they have home displays and sometimes a containers worth of fireworks is found in someone's garage ready for the 4th. There are every year "shoot and scoot" shows where in a no fireworks place someone will drop a loaded rack by the road light a long fuse then drive off to watch the fireworks and probably their law looking around Keystone Cops ish
* Sane being a state of mind, who ever heard of a firework with a mind?