I asked my colleagues about this matter and all of them were telling me to fill the SPIC exercises under both PIC and Instructor hours.
Your colleagues are correct
You are the Aircraft Commander (you may take over control at any time) so you record your flight time as PIC.
A Student Pilot In Command can only be accompanied by an Instructor (see definition below,
my bold and italics), so you must also have been acting as an Instructor and should, therefore, also record that you performed this function during the flight.
FCL.010 Definitions
‘Student pilot-in-command' (SPIC) means a student pilot acting as pilot-in-command on a flight with an instructor where the latter will only observe the student pilot and shall not influence or control the flight of the aircraft.