Career ending - should hope not.
Job ending - i hope so.
Accident - no.
Totally avoidable unprofessional conduct - yes.
Is "knocked the prop" an unlikely cause - yes.
Aircraft will NOT taxi by themselves unless, no chocks and brakes are off (or not working), mixture open, throttle open. Mags can be live but in combination with the other three the chances are quite slim . Logical conclusion, dopey tried to either move the aircraft by pulling on the prop or swing start it with throttle and mixture open probably with mags left on and stuffed it up.
Very easy for an engineer to confirm live mags so pilot better hope he isn't trying to pass on blame