Yes.
The rules are they aren't supposed to if there was no real impact to the onward segment. In this case, there shouldn't have been any impact to the LA810. So by the rules, QF shouldn't have done that.
Since QF took the SYD-SCL coupon they'll send LA the bill for the value of that specific coupon. Ordinarily on automated billing LA will then pay QF for the coupon value of that coupon, whatever that value is. LA can always stop that manually in their interline settlement if they wish to...if they do.
It's not always in a carrier's interests to take a coupon unnecessarily. LA for example, charges a lower fare overall ex-AU than QF. That means that coupon value will be lower than QF's average fare. But, if QF27 originally wasn't full anyway then it's free money. There are pros and cons.