Looking briefly at wikipedia - both events occurred during the early days of development of the bomb

The core was intended for use in a possible third nuclear weapon to be dropped on Japan, but when Japan's surrender made this unnecessary, it was repurposed for testing

It sounds like another aspect of the propaganda, to drum up fear of the non-functioning bomb, specifically fear of trying to replicate it. Yes, these guys probably died, perhaps from radiation, probably murder: does this prove that controlled, explosive instantaneous nuclear fission is possible? No.