This looks to me like some sort of mutual flying where neither pilots are instructors and it may be somewhere unclear exactly who is in control regardless of who is defined as PIC/P1.
One or indeed both would have had a civilian PPL to hire the a/c and presumably had checkouts/qualifications for the T67 to the hiring out club's satisfaction.
Both will be at the same standard of flying, aerobatics etc in the RAF.
In the gliding world this is regarded exactly the ingredients for an accident should an emergency occur- which is why mutual flying where both pilots are at the same level tends to be frowned upon and the instructor i/c the day's flying are reluctant to give approval for.
Less of a problem where one pilot has vastly more experience or say one is the owner of the aircraft.