I think the point that all the above posts seem to be missing is this:
Australia does have strict rules about visual approaches at night, and it is clear that this crew was intentionally conducting a night visual approach (not visual circling).
Other Australian jet airlines such as QF and DJ who regularly conduct night visual approaches in jets have training departments who ensure that all their pilots are very familiar with these rules and will certainly fail a check sim or check flight if they do not demonstrate their full knowledge and application of these rules.
Whilst this is an isolated incident, there apparently have been others. It appears that CASA feels that Tiger's training department may be lacking in this respect, and if it is lacking is such a basic fundamental (especially for pilots who are based at an airport into which they regularly conduct such approaches), then where else are they lacking?
I am not pointing the finger at the crew... They are obviously experienced enough, but obviously Tiger's training department is inadequate in it's training of crew who may possess many jet hours but are not familiar with the Australian requirements. It appears CASA shares that view, pending the outcome of their investigations.
If I moved to a job in a new country, even if I had 30,000 hours, I would assume that full knowledge of local regs and requirements would be a joint responsibility of myself and the training department of my airline. I would be required to read and understand the local regs, but I would also hope that my training department would ensure I understood the important ones before they let me loose in the LHS of a jet in unfamiliar territory.
Missing something as basic as Night Visual Approach requirements should be cause for concern as to the thoroughness of Tiger's training department.
P.S. You do not have to have the runway in sight to call "visual" to ATC. AIP refers.