What I think is the key is the assignment of the duty by the operator, which is different to the same person sitting on a jumpseat hitching a ride without being assigned a duty. In an international context, this is the EASA policy (CAP 804 Section 1 Part E Page 13)
Pilot on flight deck but not as P1, P2, SPO or FE not assigned a duty, they would log the time as SNY (Supernumerary).
Pilot on flight deck but not as P1, P2, SPO or FE assigned the duty of Pilot supervising Co-pilot activities, they would log the time as P2 (co-pilot).
In the Australian context, I would think given the OPERATOR has assigned the duty, and that CASA directs pilots to log flight time (CAR 5.52) "in the interests of the safety of air navigation".
The definition "control seat" does not ring a bell with me. I am not aware of any regulation that says a pilot must be in the front, left, right, aft, control, supernumerary seat in order to log flight time. Many people log flight time legally when they are asleep in the bunk.
I do not know this particular airlines manuals, however some airlines also require the safety pilot to take the control seat in LWO.