What is a research assistant in the Australian system?
Job advertisements in Australia invariably list a level.  If it says "Level A Academic" it is a postdoc.  If it says "HEW Level Something" then it is not a postdoc.  Consult the unversity's Enterprise Agreement for detailed definitions of the levels.  An enterprise agreement is the same as a collective bargaining agreement.  Note that starting pay for Level A is usually much higher if you hold a PhD.

http://www.nteu.org.au/rights/agreements