Yes that pic appears in George Greys 'Journals of two expeditions of discovery ......
Grey was a superstar of his day although nobody now knows his name however he was different in that he produced his journal or 2 journals in only 3 years. How it worked was he took his drawings as you saw with notations re color etc and gave them to an artist in London to color and produce. However the artist did not get the symbols exactly correct but never the less they were published.
For 170 years or so scholars have been trying to figure out there meaning.
The artist got it wrong.
Greys original drawing which I found in the Auckland library shows the truth. I do think it is RENCONG SUMARTRA and it makes sense as this part of Australia is so close in particular the Montgomerry islands just off the coast which is the largest reef system on the west Australian coast and a major fishing spot.
I have looked for this cave but havnt found it and will have another go next year.
I did find another cave in 2013 which has the most beautiful paintings I have ever seen and if you or your friends recoginise anything please comment.
Thanks for getting back.