Couple of things that are SOP at our place after loading the FMC, and I’m sure at most others, is a check for possible gross errors in the loading process:
1- Total distance in the FMC agrees with that of the flight plan.
2- Time to destination in the FMC agrees with the flight plan.
3- Fuel over destination in the FMC agrees with the flight plan.
If these simple checks had been carried out after the FMC was loaded at the departure airport then how could an accidental loading of the wrong destination NOT have been detected before they left San Diego???
Seems an unlikely scenario to this observer.