If you look at the history you'll see you burnt the monkeys just fine, but they were healed full (or close to it) by Arnellia's burst heal.
The key for the burst heal is that the wording changes between a 2-action and 3-action heal.
The base spell has a wording of this on targeting:
Heal:
You channel positive energy to heal the living or damage the undead. If the target is a willing living creature, you restore 1d8 Hit Points. If the target is undead, you deal that amount of positive damage to it, and it gets a basic Fortitude save.
So willing creature means if you cast this at an enemy they probably won't accept it, right? However when you upgrade to 3-action the targeting changes:
Heal:
You disperse positive energy in a 30-foot emanation. This targets all living and undead creatures in the burst.
It changes from "willing creature" to "all creature" so this will heal friend and foe alike. A 30' burst just hit everything so both the toady and monkeys received healing as well.