It is not *always* sensible to call up an airline if you notice an especially good deal.
Sometimes you might be fortunate to have stumbled upon a “fare error”. While this is not the case here, alerting an airline to such an error (which will often be honoured) can spoil the party for others….
BA is able to charge more because it is able to offer a consistent fully flat bed in Business Class. Qantas is not yet in that position, and is also suffering from the fall out from the exploding engine issue.
The matter is moot, however, as revenues are shared between QF and BA on this route.