It's not that they're afraid of things they don't understand. It's that there is a certain type of person they generally don't like. In this case it might have been a man that had some sort of intellectual curiosity, maybe a bit eccentric. And they will use their ignorance as a weapon against those people.
The police department knows full well they can determine whether this was a bomb or not. It's within their ability to interview every person he interacted with to find if he claimed it was a bomb at any point. Instead of doing that they will use their lack of knowledge to allow falsehoods to move the investigation.
It was within the ability of the staff to determine the monetary cost of this man's actions. In the very least they could compare the electricity bill during a month he was running SETI versus the next month when he was not. They could calculate the power consumption of the machines.
It's not that they are afraid of knowing. But that knowing or admitting the truthfulness of the facts makes them less powerful as people.