As alluded to by previous posts, a lot of this comes down to what was briefed amongst the crew. If they did not brief circling, they shouldn't circle, as a contingency or otherwise.
Additionally if ATC weren't given a heads up on the possibility of circling, it would be difficult for them to plan actions in the even of a missed approach. If the crew announced "...going around" with no further requests/requirements ATC could not assume the pilots would climb to circling altitdue. they would have to assume (unless told otherwise) that the aircraft would carry out published missed approach. Published missed approach altitude may not have been acceptable to ATC reference other traffic, airspace etc.
Besides, CASA suspended so that they can investigate which should clarify all of this...