If an odor gas was called in, the fire department would have been dispatched to investigate - much quicker response than the utilities companies; fire companies carry Multi-gas meters to detect levels.
As for the people hammering the side walk no clue.
Natural gas will follow the pipe route under the ground as well as into the air, especially if the pipe was leaking for a while and not vented to open atmosphere. In essence followed the pipe path into the building or close enough to the building to build up inside.
It's not that uncommon a thing to happen.
Fire Rescue Fag