Sounds like they bought a “quarter stick” in a state where it was legal, and got caught with it in a state where it is not.
States decide at what point a firework is OK for a civilian to own and when it’s a deadly explosive, its the grams of blackpowder or flash that determines legal status.
When the bomb squad destroyed it, all the witnesses said it sounded like a firecracker.
I was mistaken- they had smoke powder in plastic pipes.