An aquaintance who is currently a senior Public Servant in Canberra once informed me that they were invented by Canberra Bureaucrats in the early 70's. And so were the 'traditional smoking ceremonies'.
Make of that what you will.
My own opinion is that there were around 500 different Tribes of Indigenous Peoples existant around the time of the arrival of the First Fleet, that they
all had these 'traditional' ceremonies, ie 'Welcome to Country' and 'Smoking' is indeed somewhat hard to accept.
Considering also, that it is well recorded that most Tribes simply did not get along with each others and quite often engaged in some fairly bloody battles with each other!