You can expect a standard knee jerk reaction to this incident...the use of non-standard levels will probably be henceforth banned.
There are probably multiple factors to consider here.
First is the "can do" culture that has sprung up in Oz over the past 20 years.
There is also the push from management that the controllers have to facilitate their "customers" as much as possible, often to the detriment of safety.
I have no idea of the circumstances of this incident other than what has been mentioned here, but making a stab at it anyway, IMHO controllers in Oz are trained these days to pretty much say "yes" to most requests...in the old days some were trained to think "no" and then look for a reason to justify it. If no reason could be found, he got the level/routing etc.
There has to be a happy medium there somewhere.
The "back of the clock", disengaged workforce argument I do not think is the reason (although I hasten to add, I do not work in Oz anymore).
We have had two nose to nose STCA (Short Term Conflict Alert) sorted incidents in my patch in Europe recently, in full radar coverage, with a fully engaged and well rested workforce.
Sh!t happens, humans make mistakes, and happily all the holes in the cheese didn't line up.
Good work from the pilots for having good situational awareness.