So your instructor wants you to NOT land an aircraft with a fire of unknown size at an airport that WILL have extensive Fire Fighting capabilities because when you evacuate a few pax may end up with sprains and possibly a couple of breaks in order to throttle up, increase eng temp, increase EGT, increase fuel flow, take you away from the safety of the airport where Pax will have NO opportunity to escape in order to attempt to put out the Eng fire using equipment that MAY extinguish the fire but more than likely will be overwhelmed if the fire is anything more than a minor, contained burn which, if it fails, could well end up with all Pax deceased if the fire penetrates the wing or fuselage tanks prior to your return to airport unless you try a field landing which would also end up with more serious Pax and crew injuries....
Because that makes sense...