Hi,
Since there was no evidence that the engine was actually overheating, most likely it was an electrical issue. Commonly, low voltage will cause the electrical systems to go haywire. Since the battery was recharged and it's running properly, it could have even been a loose or corroded battery terminal that was cleaned up and tightened when the mechanic recharged the battery.
At this point, I would probably confirm the alternator is working and charging the system. If it is and terminals are clean and tight, it should be fine.
If you want to test the alternator, here is a link that explains how it is done:
https://www.2carpros.com/articles/how-to-check-a-car-alternator
Here are a couple other links you may find helpful:
https://www.2carpros.com/articles/how-to-use-a-test-light-circuit-tester
https://www.2carpros.com/articles/how-to-use-a-voltmeter
https://www.2carpros.com/articles/how-to-check-wiring
Honestly, since it is running okay and it was checked, you should be fine. If, however, you have other questions or need help, let me know.
Take care,
Joe
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Monday, March 2nd, 2020 AT 5:48 PM