As Steve says, this song is unequivocally set in Australia. And yet it's only an apparently later version that names a real Australian location (Hawkesbury), with the fuller (probably earlier) versions giving similar sounding but different names. And it's still at best only informed guesswork as to whether the person who first made it was a sailor or a returned convict (who might have been familiar with the Hawkesbury River) or a professional broadside writer; and whether it is a total fantasy or based (closely or loosely) on a real encounter.

I think my money would be on a broadside writer who either had previously been a sailor or convict or had got the tale from such a man, and on the tale having some basis in fact.

Maybe a chap in Norfolk boasting about his real or fictional sexual exploits but, to avoid embarrassment, saying ("Oh it wasn't in these parts: it was when I was down under, by the Hawkesbury River, and she was a native girl".