Voltage detected on gas pipe
I agree with Ed Beal. The technician had no idea what they were doing.
The gas pipe is required to be bonded yes, but the equipment ground that serves the electrical circuit for the furnace is allowed to be the sole means of that bonding.
From the 2017 National Electrical Code (also in earlier versions)

250.104
(B) Other Metal Piping.  If installed in or attached to a building or structure, a metal piping system(s), including gas piping, that is likely to become energized shall be bonded to any of the following:
(1) Equipment grounding conductor for the circuit that is likely to energize the piping system.
...

You said --

However, when tested at the furnace using its ground there is no voltage at all on his multimeter.

This tells me your equipment grounding conductor for the gas furnace circuit is in good condition.
A millivolt signal to a screwdriver stuck in the ground is not a reliable way to do earth ground testing.
The Utility should immediately restore your service and that technician needs to be properly trained.
Good luck!