I'm blowing things a bit on this comic, but fire is everything but friendly in this game. While you can't spam fire pots (you only have one) the average lifespam of a soldier isn't long so they throw they fire pot, die and respawm with a fresh one.

Friendly fire is always on so isn't uncommon for your ally put you on fire while you are busy trying to fend off 2 enemies.

Fire won't kill you most of the time but will hurt you enough for a convenient arrow to finish the job.

All in all, a pretty accurate simulation of medieval warfare.