Sailors from Makassar already knew about Australia.
These are sea cucumbers, or what Indonesians today called trepang or teripang. They’re considered a delicacy and even believed to have medicinal values. You can find them in traditional Chinese food stores in its dried form. It needs to be soaked in water before cooking if it was dried, though.
So, these sailors and fishermen from Makassar used to export these things all the way to China. Where do they get it? Well, from the waters off the coast of Australia. They called it, Marege, which refers to parts of northern Australia (specifically around Arnhem Land) where the sea cucumbers there are of high quality. There has been historical evidence of camps in Australia that these fishermen constructed while they harvest the sea cucumbers. On land, they would spend months boiling and drying these sea cucumbers as a method of preservation before making the journey back to Makassar with their catch. There are also evidence that points to the fact that they traded with the aboriginal tribes in Australia. Even today, sea cucumbers remained as one of Australia’s maritime exports.
So yes, Europeans discovered Australia in 1606. Others, like the sailors from Makassar, already knew about it for some time before that.