I've recently triggered QF with this, as well... I'd seen it happen a handful of times in the past, even when DSCs were being given out to all and sundry, but this is the first 'BSC' (Bonus Status Credits - not necessarily double SCs) offer I've had in some time.
I was performing a search of fares for my boss, to DFW and also PHL, on the 21st January, and tried a few combinations and dates, all for mid-February. Nothing was booked - he just wanted a quick indicator from his resident travel guru. 7 days later on the 28th January I received an e-mail from Qantas with the subject "Fly to Dallas Fort Worth, get 50% more Status Credits". Coincidence? I think not.
Thankfully, the ONLY reference to Dallas is in the subject line, and it is open to all QF marketed flights (QF flight numbers), and so while I'm not headed to the U.S., I am planning some INT travel for March, and will now likely take advantage in the period.
Cheers,
Matt.