While wikipedia etc state that a bomb contains a destructive substance and is designed to explode, the 'store' dropped from the DC4 was by modern usage a BOMB.
A 1000lb Inert Bomb, with no explosive, is still a bomb. Low altitude releases can result in bounce and the splash can down an aircraft, both shown in this programme.
Regardless of whether it was a replica explosive bomb or this scaled replica store it was still capable of downing the DC4.
Had the release mechanism of the rotating store failed is some manner it could have been catastrophic.