They didn't solve the problem
When multiple parts interact together, we have to repair the known-bad parts before we can diagnose the system further. Your coolant-temperature sensor and thermostat are now working correctly, which allowed us to pinpoint the problem to your instrument cluster. It's likely your car is not overheating, but the gauge will need to be repaired so that it displays your coolant temperature accurately. We'll be happy to help when you're ready to complete the repairs, Isaac.
- Toole's Garage Stockton