It could be that we're not getting the full story and/or that the terminology used is incorrect and/or mistranslated. Would not surprise me in the least really. It might be something like the brass shell casing from a large unitary cartridge... or it could be a projectile... or a non-fixed propellant housing... or a guided missile casing... or anything. Could be that he didn't realise what it was, or that he thought there was no fuse in it (no fuse in a shell = no bang.... unless the filler degrades that is...)