Yeah but then there'd be complaints about the cost.

It's not paranoia. The SS is required to investigate everything even off handed comments.

"If you heard what you thought were explosions, who would you call Dan?"

What would you be calling for? You didn't see anything. Why tie up the 911 line just to gather info?

"911 what's your emergency?". "I heard a loud boom somewhere and I was wondering if it's something I should be afraid of."