Are you sure that's not a BA fare?
Definitely Q on matrix front screen and when you process it the fare does look to stay Q badged and the flight numbers appear to stay as Q for SYD/HK rtn.
But then it says (see in red) BA fare - either way it is cheap but maybe status credits at risk etc.
ITINERARY
Sydney (SYD) to London (LHR) - Mon, Jan 19
Qantas Airways Ltd. 127 Dep: 11:25AM Arr: 5:45PM 9h 20m Airbus A380 Coach (O)
Layover in HKG 5h 45m
British Airways p.l.c. 26 Dep: 11:30PM Arr: 4:50AM 13h 20m Airbus A380 Coach (O)
Tue, Jan 20
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London (LHR) to Sydney (SYD) - Tue, Feb 17
British Airways p.l.c. 11 Dep: 7:10PM Arr: 3:55PM 12h 45m Airbus A380 Coach (O)
Layover in SIN Wed, Feb 18 4h
Qantas Airways Ltd. 82 Dep: 7:55PM Arr: 6:50AM 7h 55m Airbus A330 Coach (O)
Thu, Feb 19
FARE AND BOOKING DETAILS
Provide this information to a travel agent to help them match the fares found.
Make sure to provide the exact booking and fare codes shown.
Fare 1:
Carrier BA OLSALEAU SYD to LON AUD361.22
Passenger type ADT, round trip fare, booking code O
Covers SYD-HKG (Economy), HKG-LHR (Economy)
Fare 2:
Carrier BA OLSALEAU LON to SYD AUD355.00
Passenger type ADT, round trip fare, booking code O
Covers LHR-SIN (Economy), SIN-SYD (Economy)
(YQ) AUD413.00
Australian Passenger Movement Charge (AU) AUD55.00
Australian Int'l Passenger Service Charge (WY) AUD27.62
(YQ) AUD288.00
Australian Int'l Passenger Service Charge (WY) AUD27.62
Singapore Passenger Service Charge (SG) AUD8.10
Singapore Passenger Security Service Charge (OO) AUD2.70
United Kingdom Air Passengers Duty (GB) AUD184.60
United Kingdom Passenger Service Charge (UB) AUD85.60
Subtotal per passenger AUD1,809.24
Number of passengers x5
Total airfare & taxes AUD9,046.20
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Fare construction (can be useful to travel agents)
SYD
QF X/HKG
BA LON Q5.80 331.08OLSALEAU
BA X/SIN
QF SYD 331.08OLSALEAU NUC 667.96 END ROE 1.072221 XT 55.00AU 55.24WY 184.60GB 85.60UB 2.70OO 8.10SG 701.00YQ
This ticket is non-refundable.
Changes to this ticket will incur a penalty fee.