Here is an interesting question this brings up with me. Just because you have a talent that applies to damage like in this case do you have to use it? I mean it is your talent you should have control whether it comes into play or not. That is just my two cents on the talent.
Here is the thing...There are some Talents that you can "Control" those are the Active Talents...You have to tell the GM that you are using said Talent...BUT if it is a Passive Talent, like Lethal Blows, you have No Control and it just activates when the conditions are met.