I predict he will create "armor". Then everyone can just stand there while the enemy pokes them with sticks. If they have some sort of super basic armor (I'm assuming a cloth over the eyes since we all know that if we can't see the enemy they can't see us), maybe he'll invent iron and since they seem to be stone age (you'd need wagons and stuff to haul metal for a bronze age), so the enemy won't be able to do anything. The villagers can literally walk through slaughtering with not even an injury.