Doesn’t make sense. Why would a prisoner be left in armor at all?
I’m just trying to imagine the scene here... just one scenario that may or may not have anything to do with reality; I’m NOT a combat vet... So... The battle’s over. You’ve got dead and injured lying all around, friendlies and enemy alike mixed together. You want to secure the battlefield as quickly as possible to prevent someone jumping up and chopping your head off, or worse, your commanding officer’s head off. Removing everybody’s armor is time-consuming. So... just go through and quickly shackle all the enemy, dead or alive. Deal with them later. Only in this guy’s case, later he was dead.