if it is a standalone SYD-MEL booking , I would have expected the allowance to be 1 piece of maximum 23kg
If you have an allowance of 30kg, that is surprising ; I would only have expected that if it was part of an international journey ( e.g. LHR-SYD-MEL )
The manage booking page would not look the same as the link - that is a link to the general baggage allowances
regardless - where there is a weight allowance rather than a piece allowance, the only limit per bag is 32Kg and your screenshot clearly shows a weight allowance