When it comes to government reps that field calls like this, there's some variation of a formula saying for every one phone call translates to X number of people that feel the same way but do not make the call. It used to be different weightings for someone calling vs writing a letter. Either way, it was more a statistics reaction. Not sure if this comes into play or not.

It could also be that the single person that did complain happens to be a close friend or even related to someone else powerful, or is just influential in the area in other ways. That tilts the weighting as well.