This is true, but misleading
Temperatures over 50 were routinely measured in Australia in the 19th century, but it was due to the fact that Australia hadn't modernized its weather technology until 1910, which is when "official" Australian heat records begin.
The pre-1910 data have not been “wiped from the record”. They are still available on the Bureau’s website, but are not included in the official record because they cannot be compared easily with modern data. http://theconversation.com/factcheck-was-the-1896-heatwave-wiped-from-the-record-33742
The year 1829 stands out as particularly warm. Although the temperature observations are to be treated with caution...Although the development of this dataset represents a significant advance in historical climatology in the Australasian region, there are unavoidable limitations that must be considered. Observer biases and remaining inhomogeneities mean that the observations are of poorer quality than modern meteorological records, and they should be interpreted with caution. Particular care must be taken with the temperature observations, which are especially sensitive to changes in exposure, and monthly rainfall totals, which have not been examined for undercount biases https://rmets.onlinelibrary.wiley.com/doi/full/10.1002/gdj3.19
In short, don't take Australian temperature recordings prior to 1910 at face value.