The RBA is forward looking, not backward looking. The GDP numbers are what has happened, and are therefore not relevant to the cash rate in the future. Current conditions and past conditions have a lower weighing than expected conditions.
The future is likely to be better than the past judging by leading indicators such as business & consumer confidence, Westpacs leading growth indicator, job ads, etc. By raising early the RBA is attempting to prevent an asset price bubble and high inflation.
If they raise early, then it's less likely that they will have to raise as high.