>>82426167
It's not a war crime.
It's only defined as one if you kill someone who shows clear intent to surrender, and that clear intent is acceptably obvious to the person accepting the surrender.
Because the drone pilot can't capture the soldier; can't confirm or ensure that the guy on the ground won't just run away and join his comrades after he's spared, the drone pilot is fundamentally incapable of determining the intent to surrender and so can't be held responsible for killing the individual. This same rule applies to aircraft in general.
Clear intent is the defining factor and aircraft can't determine clear intent unless there's friendlies on the ground.