1994 Vauxhall Corsa Themostat blown, could mechanic have do

I dont know, I think just the thermostat, it took him bout an hour. Car didnt overheat. Temp gauge that they replaced works fine. But everything to do with my cooling system worked fine before I gave it to them.

No its not new, I had to bring it back to them again to replace thermostat because I figured out it was blown after they replaced the temp sender switch. I think you may have mis understood my forst question. On replacing the alternator they broke the switch, I brought it back to them and they replced it, I drove to work and still temp gauge not working so brought it back, they told me thermo was blown, but it wasnt blown before I initially left it in with them, so blew in the two days that they replaced alternator, then switch. What I am really wanitng to know is if the thermo couldd of blown because I was driving with a broken temp sender switch or could the mechanic of blown the thermostat when woking on the car.
He did electricute hinself when checking the temp switch and burn himself when replacing it which doesnt give me much faith in him.
He got help to change the thermo as I watched him do the end of it. I watched them put in new temp swithch, he just unswrewed the old one and screwed in the new one. Done, it took about 30 seconds.

Could he have shorted the thermo and blown it or revered polarity when changing the alternator or somehow caused some other problem that blew the thermo. I am a student electrical engineer myself but know very little about car engines as its my first car.

Thanks so much for your help.