I think at least one Australian D/E subs has "sunk" a few US and other ships during RIMPAC exercises, including a US Aircraft carrier. Not sure how much emphasis you put on these Exercises.
Either way, the US would not have liked the fact that the Australian Sub managed to get close enough to "potentially" do damage.
All Australian sub captains are Perisher trained and a Collins sub (when working properly) are far superior to cheap Russian and Chinese knock off subs, so it's not a suprise one could get close enough to sink a Nimitz CVN. Annoying the Yanks is an added bonus and the same treatment would be given to a QE carrier if one ever pays a visit to oz.