I asked Yoan Donev who works in the Central Laboratory for Conservation and Restoration at the National Historical Museum in Bulgaria to measure the tin can and also to give me an opinion on the hypothesis of the can being used as a grenade.
"I think it was a regular can, not a grenade, because if it had been exploded or even just enlarged by the contents spoiling, there would have been signs of inflation. Also the edges of the elongated cut are inverted inwards (possibly forced with a blade), where on explosion they would curve outwards."