Here is the CAR;
5.52 What must be recorded in a personal log book?
(1) The holder of a flight crew licence, a special pilot licence or a certificate of validation must record in his or her personal log book:
(a) the holder’s full name, address, date of birth and aviation reference number; and
(b) any information about each flight undertaken by the holder that CASA directs be recorded in the log book; and
(c) the time spent by the holder practising simulated flight in an approved synthetic flight trainer.
Penalty: 10 penalty units.
[Note It is an offence against regulation 283 for a person to make a false or misleading statement in his or her personal log book.]
(2) CASA may give directions in Civil Aviation Orders setting out the information about each flight undertaken by the holder of a flight crew licence, a special pilot licence or a certificate of validation that the holder must record in his or her personal log book.
Here is the CAO;
9 Log books
9.5 For the purposes of subregulation 5.52 (2), the information about each flight must include:
(a) the date of each flight; and
(b) the type of aeroplane flown; and
(c) the registration marks of the aeroplane flown; and
(d) the point of departure and the destination of each flight; and
(e) the nature of each flight; and
(f) the time flown on instruments; and
(g) time flown in single and multi-engined aeroplanes by day and by night; and
(h) in accordance with subsection 10, the capacity in which the person flew the aeroplane
10.9 Instrument flight time may be logged by the pilot monitoring or providing input to the
autopilot/auto-stabilisation equipment when it is engaged or by the pilot manually manipulating the controls when the aircraft is flown by reference to instruments under either actual or simulated instrument flight conditions.
Note Instrument flight time shall only be logged by 1 pilot at a time.
Quite clearly only one pilot may log IF time, either the student is logging it or the instructor is, not both!
The pilot log book page on the CASA web site was issued via an AIC which holds the same legal weight as the AIP. However as correctly stated it is just CASAs' interpretation and governing stance on how things should be.