Thermostat And Thermostat housing replacement

I have a 2003 Ford Escort ZX2 with 54,000 miles on it with a 2.0 Ztech engine.

I noticed a puddle of antifreeze underneath my car and after further investigation determined it was coming from the thermostat housing. Brought it to the Ford Dealership for repair.

They did the repairs and I left. Approximately after driving 2 miles from their shop my temperature gauge went all the way to HOT.I mean all the way over almost into the speedometer.

I pulled over and the car was not hot.

I brought it back to the Ford Place. Thinking it was something they had done while doing the repair. After them looking at it a second time they informed me that the temperature sending unit had gone bad.

I thought it peculiar that it would go bad immediately after their repair. And asked them what caused it to go bad. They said that it was a short circuit in the wiring that caused this and that it could have happened at any time.

This certainly doesn't seem right or logical to me especially after their repair had to do with essentially the same thing.

Is it something they could have done in their replacement of the thermostat and thermostat housing to cause this to go bad?

I already payed them $351 for the initial repair and now they are wanting me to pay for this second repair which I sincerely believe was their fault.

Could someone please tell me if I am wrong in my reasoning?

Many thanks!