This stuff is propellant. If not confined into a cannon barrel where the pressure can build up, it is not going to cause an explosion.
A big hot fire, yeah, it could happen. But that would not endanger the countryside for miles around.
I think that the mass evacuations were a bit of over reaction, although I can understand that nobody wanted to be the one who said "Aw, it's safe in your house a mile away."
The M6 propellant has a reputation for going high order (exploding). The stabilizer in the mix can only absorb or neutralize so much nitric acid and the propellant will become unstable after time. Once it starts to heat up or you see a reddish tint on the labels or lids, about the only thing you can do is to put it under water.