A little bit more inside information.
Pax had travelled from Portugal with BA and bags were checked through to HKG.
LHR to HKG was on CX. So if the passengers knew they were going to fly a different carrier, surly alarm bells tell you, "what about my bag"its not on my flight.
This problem was discovered about 2hrs out of LHR. By now it was 0100am in LHR so not alot of ground staff to help out as to were pax were. Eventualy found out pax were on BA.
Even 1 percent of doubt as to why pax on 1 airline and bags on another is suffice to make the correct decision.(was this a planned mistake)
However much people Knock both CX and BA, there probably 2 off the best airlines in the world.
By the way the aircraft was abeam SVO when decision was taken to turn back.
SVO is hardly suitable alternate for CX at about 0400am in the morning.
At least LHR had time to sort out hotels, and suitable facilities.
At the end of the day. if your the driver and your carrying dodgy bags, would you rather get home,or return back to a suitable port.