My Dad did always tell me not to play with fireworks, he said something like this would happen.
I am somewhat confused. Ammonia Nitrate is an explosive chemical particularly in a confined space where temperatures and pressures can get to a critical level of explosive detonation via the shock wave through the mass of Nitrates.
You can take a pile of this stuff and drop it on the ground and drop matches into it and nothing will happen.
I am confused.
Ground level view starting at about the 56 second mark.
Looks and sounds like fireworks to me...
https://www.youtube.com/watch?v=yNH4eE3RYUM