Definition of public duty

Last year supreme court judgment (Ramesh Gelli vs CBI) in that Court dismissed hi crinimal revision application stating that he is public servant u/s 46A of BR act, he hold an office as he was chairman of Global Trust Bank and also he was discharging public duty. My question is whether following person/institution covers public duty 1. Principal and Employees of Educational Institution without Govt Aid. 2. Director and employees of Private companies dealing with public like private hospitals, finance company, super markets like big bazar & D mart etc 3. Contractor of government and PSU contracts.