I think corspes must always be plundered. The items shouldn’t be marked as stolen. Just check in your inventory. If there is a red hand in the icon it’s stolen, but this shouldn’t be the case here.
there is an arrow on the Plunder-key. Which means the items will be marked as stolen. Normally there shouldn’t be an arrow when targeting a bandit. Because the bandit tried to run away without fighting?
Attacking him will also reduce my reputation