It's not fuel contamination issues at all. It is related to the fact that a shipment of overseas-refined aviation fuel, failed to meet specifications for all the tests for fuel refined to Australian Fuel Quality Standards, as defined in the Fuel Quality Act 2000.
Fuel Quality Act 2000
The fuel testing covers a range of potential issues that cover everything from allowable water content (yes, there is an allowed level of water content!), through to lubricity levels, corrosion inhibitor content, allowed and disallowed additives, levels of various metals content, and even levels of Fatty Acid Methyl Esters (FAME).
The testing is usually done by independent laboratories, to ASTM D 1655 or DefStan 91-91 standards, and to check against any other specific legislated requirements under FQA 2000.
Believe me, the testing is thorough and is designed to catch out refinery slip-ups (refinery cross-contamination is common), dodgy refinery operators substituting disallowed additives, or straight-out contamination from the oil tankers tanks or sloppy handling.
A failure to meet any of the specified parameters means the entire fuel shipment is not allowed to proceed until it does meet the specified standards and parameters.
The problem we have in Australia (and one that is raised and hammered regularly, without any pro-active response from politicians) is that Australias fuel reserves fall far short of what is required, if a major natural disaster, major obstruction to shipping, or some other catastrophic event such as a refinery explosion, results in a severe curtailment of fuel supplies for an extended period.