It is strange, because unless the caster cast it on themselves, it was a cheat.
(Re-)read the definition of Range:Voice (AM p 112). (It's just one paragraph)
"The range is based on the distance that the caster's voice carries..."
So, yes, a whisper carries a very short distance, and "silence" not at all.
In situations like that, a SG has to weigh "detracting from the plot" in the immediate situation vs detracting from the game itself in the long run. In my experience, the "harder" the rules of the world, the more believable and enjoyable it is. If the rules of magic keep bending and breaking to make things "easy" for the story, then it's more like an amusement park ride, where you know you're going to get where you're going, no matter what.
I have had some quiet magic mages and they basically had to almost forgo most voice spells becuase it went against their casting style. THankfully both have alternatives, one uses flexible formulaic to up it to sight or drop it to eye most of the time, the other is holy maga and uses presense (holy Magus range).
I am a dork
I do admit to playing fast and loose sometimes to get the story moving along, but I do like sticking to the rules and making sure they are applied evenly to both the antagonist and the protagonist. To me, that's where I get my sense of realism from.