Thanks! And you're right that that description is inconsistent: you'd remove dice when A) the sum of the result is less than the spell's resonance (you'd remove all the dice in this case) or B) when the result on a single die is higher than the average roll for whatever die you're using (you'd just remove that die in this case). That said, the content of the engine doesn't particularly care whether you use "higher than average" or "lower than average" in case B. I would recommend the former over the latter in cases where your implementation/interpretation of some of the resonance trees is scaling other effects off the result of the casting roll.
