Bandit intercepted my army, lost all soldiers

I sent my army (15 recruits and 3 bowman) against a bandit camp of 10 scavengers.

They were intercepted before reaching the camp but the battle result said that only 3 recruits and 1 bowman were involved in the battle. I lost the battle, with an injured general, but my entire army was lost somehow.

Is this a bug?

No, look at the red areas when you click on a bandit camp, if your general strays into that, he will be intercepted.