Working Holiday Makers are taxed at different rates to resident tax payers.
In the 2017 financial year, separate tax rates were applicable for Working Holiday Makers' income. Prior to this, the income was taxed based on their residency. This information is mentioned in the following article;
https://www.ato.gov.au/rates/individual-income-tax-for-prior-years/?page=3
Please contact the ATO if you require any further assistance on this matter.