Police in north eastern Sylhet had thought Sunday's explosion outside a cinema, was the result of a homemade bomb going off by accident.
But investigating officers said on Monday they now believed the explosion was caused by slum dwellers trying to extract lead to sell from a canister.
The dead were named by police as Anwar Husayn, 45, and his 14-year-old nephew Jalil. Seven others were injured including Husayn's pregnant wife.
"This was an accident not an act of terrorism," Deputy Inspector General of Police Mahfuzul Haq said.
"This man bought a canister from some children for 130 taka (2.16 US dollars) and he was trying to break it open with a hammer to take out the lead so he could sell it for a small profit; he was not a terrorist," he added.
It was not known what type of canister the dead man had been trying to open although unofficial sources said it might have been a mortar shell from a nearby military base.
Sylhet, a city of one million people, has been the scene of several blasts since May. At least seven people have been killed and more than 250 wounded, including British High Commissioner Anwar Choudhury.
The deadliest blast in Bangladesh's recent history occurred at an opposition rally in the capital Dhaka on 21 August, killing 19 people and wounding 150.