My reading of the article is that it was a very large firework, rather than some kind of professional explosive device stored fused with a blasting cap. Given the power described I stand by my original comments regarding storage of explosives.
The article cited speaks of "dynamite," which of course could be a generic term (anything highly flammable) used by the reporter; it might well have been a road flare, signal flare, or some such which could cause damage if handled carelessly, as this one evidently was.
Reminds me, I have a couple of nautical signal flares that I should dispose of properly - take to the local FD, most likely.