Damaged Alternator and Charging System.

1999 Camry LE Automatic, Mileage: 170000Km
I took my vehicle to one of the local Toyota Dealerships for a Detailing package. The package included cleaning an d shampoo of the engine compartment.
The day that I picked up the vehicle I was able to drive it for about 1 hour before returning to work. Later that day the car would not start anymore. Before it was towed back to the dealership I was told that the alternator was damaged and the battery discharger. The technician at the dealership confirmed that after running a diagnostic test. I am trying to understand if the damage could have been caused by the cleaning of the engine. The person at the dealership is arguing that the alternator is fully sealed and that the fault occurred due to the alternator being old and that they see things like that happen all the time. A mechanic friend of mine; however, tells me that if the electrical components in the engine are not covered properly during cleaning, damage can result easily to the alternator. Your opinion in this matter will be greatly appreciated.
Best Regards