Outside of the cities, this isn't true - Australian speed limits and average driving speed on highways is much lower than basically anywhere in Europe.
Inside cities, Australia definitely does have higher average speeds than inside most European cities though.
This is true of urban areas but not expressways. Motorway limits vary from 120 (Spain) to 140 (Poland) with Germany having sections of unlimited autobahn.
Inside cities, Australia definitely does have higher average speeds than inside most European cities though.