I see your warrior has a shield. Have you learned Shield Expert by chance?
There's a known bug with shield expert causing weak range attacks to heal.
The mechanism of action is that shield expert reduces damage by adding health to an attack (6 attack + 4 heal = 2 damage, type of thing). So when a range attack is very weak (say weak range fire attack against high fire resistance), the math ends up being a net gain for the player (e.g. 3 attack +4 heal = 1 heal).