Australia was not as isolated as this question suggests. There is evidence of trade and contact with New Guinea and, probably from some time in the 17th century (though there are scattered indications of earlier visits), the north coast was regularly visited by Makassans from Sulawesi who came in search trepang. There is always more to say, but [h/t u/hillsongoods] these earlier responses offer and initial guide to these early contacts:

There's a section of AskHistorians' Oceania FAQ titled 'Asian interaction with Australia'. Linked to on that FAQ are a great post by /u/PangeranDipanagara about Makassar fisherman looking for trepang in Northern Australia, and a succinct post on the topic by me, /u/mikedash, which links to a much longer essay that I wrote on the topic.

I think I've answered this question before, but Australia was probably discovered at least once by Polynesians before the European discovery.

In the 1928 Christmas holidays the newly founded 'Anthropological Society of New South Wales' went on a trip to Dark Point (north of Newcastle) where among some other remains they found a basalt adze head that they considered to be of 'undoubted Polynesian origin' (JPS article, picture on the next page). Microscopical examination was inconclusive about the origin, but in 2014 the adze was re-examined with modern technology, and was shown to be pretty certainly from Norfolk Island stone. Post-European transport is possible, but both authors consider it unlikely.

And a brief history of Norfolk Island. Norfolk island is a small island in the ocean in the middle of New Zealand, New Caledonia and Australia, and a long way from any of them (about 700 kilometres from NZ or New Caledonia, and twice that from Australia). It was first settled by Polynesians either directly from New Zealand, or via the Kermadecs, in the late thirteenth century; very shortly after New Zealand itself was discovered. This settlement lasted for a while, but by the time Captain Cook arrived in the late eighteenth century, Norfolk Island was abandoned. This is probably due to a relatively poor situation for horticulture, which meant there wouldn't have been a lot of food after all the marine mammals were killed. A number of New Zealand's 'outlying' (some of them are actually really far) islands were settled shortly after Aotearoa itself (the Chathams, Norfolk Island, the Kermadecs, even Enderby in the sub-Antarctic Auckland Islands), but all except Rēkohu (Chatham Island) were no longer inhabited when Europeans arrived.

It's certainly possible that at least one voyaging canoe turned up on Australia's east coast some time perhaps between the 13th and 15th centuries. It was a very long trip, a week with good winds, rising to almost twenty days with bad, but other long trips had been made before. Norfolk Island would not have been reached in less than three days, and unlike Australia, which is pretty hard to miss, if you were heading in a direction even a couple of degrees off the correct one then the island would be well below the horizon as you passed. What happened to any voyagers who made it is obviously unknown, but the climate and landscape were so different that it probably would not have been possible for any attempted settlement to survive while employing the tradition Polynesian lifestyle, regardless of how the local people reacted. The authors of the second paper suggest that Polynesian influence is behind the distribution of a particular kind of Aboriginal fish-hook. That's obviously super speculative, but if it was true would indicate an at least slightly sustained period of contact and cultural exchange.

Sources are the two papers I linked, and Tangata Whenua an Illustrated History (the bit I used was written by Atholl Anderson, who's also done a lot of papers on the archaeology of the islands settled from Aotearoa).