Alliant is doing two things, IMO:
Covering its butt for the extreme conditions where smokeless can explode. I heard of a factory blowing up a few years ago, and all the knowledgable people working there strenuously denied that their oxidizer product was explosive. Volatile, yes, as it easily breaks down to release O2, but not explosive. It can and often does make big "booms" when combined with a fuel. Then someone found a textbook that listed the extreme conditions which make explosion possible without an accompanying fuel--large quantities and either extreme heat or severe shock. Kablooey!
The second thing Alliant may be doing is covering its butt for the very real possibility that some careless nut will store his or her powder under extreme heat or whatever it takes for the Nitroglycerin in their double-base powders to separate out. Technically, it's not smokeless powder any more, but a mix of nitrocellulose and what we might call free nitroglycerine. And that stuff IS explosive...