Hi,
If the wire was knicked it could have easily blown all those components.
Taping the wire may have been sufficient but he did the right thing in replacing it as its hard to tell how weak that wire is and you really do want solid wires without splices in them going from point A to B especially when they are in an area that is not easy to get to, he probably saved you a headache down the road.
Running wire through a crawl space is acceptable for low voltage wiring. The typical thermostat wire is jacketed for that installation and a compromise in that jacket can cause problems later on. The HVAC service man did exactly what he should have done and in your best interest.
Thanks
Mark.
Journeyman Technician
UA Journeyman Pipefitter , HVAC, Refrigeration, DDC controls. 26 years.Commercial & residential
Here is some additional info from an electrcal expert here.
"Also the plumber is not licensed to run gas piping. He is not a mechanical contractor.The electrical code requires the thermostat wire to have the CL2 or similar jacket on the wire. If this is compromised it would violate the electrical code."
Mark