If pilots are using this definition to define a duty period, it is wrong!  

This is not a correct definition for a pilot's duty period:

Duty period means the period of elapsed time between reporting for an assignment involving flight time and release from that assignment by the certificate holder. The time is calculated using either Coordinated Universal Time or local time to reflect the total elapsed time.

That is for a Flight Attendant under FAR 135.273, which is not applicable for Flight Crewmembers (i.e., pilots)

For pilots, ANY work performed by the pilot for the certificate holder is considered duty.  Thus, a duty period is the period of time from when the person began the day working for the company to when that person ended working for the company.   Simple.   Has nothing to do with "an assignment involving flight time".   You are on duty if you are working for the company, whether it is flying, washing the CEOs car, mopping floors, taxxiing to/from a broken helicopter, deadheading on an airline/bus/train/uber/pov/etc travelling to/from a base other than your domicile (assigned base).   It is all duty!