I'm confused.

1) How did "Essequibo River" come into this topic?

2) What does it really matter what Shanty.org thinks. I don't imagine they have any data more than anyone else (?). They are just presenting the song and providing a customary background filler. One could ask why it

3) Hugill's seems to be the only original volume to present the song. (?) And yet, the tune on Shanty.org is not Hugill's.... well, not his book version. If Hugill sang it differently on his 1962 recording that followed the book (which I've not heard), then one must wonder why he wrote it that way in the book.
Shall we assume it is a "revival" tune?—which is valid in its own right, but does not tell us anything about the history.

4) Coastal Guyana can be considered as part of the "Caribbean" world.

5) "Nobody has..." Nobody where? Who is nobody? The quote from the guest Mudcat poster is a strawman. There is plenty of evidence, not to prove definitively, but to "support conjectures" that the song originated in the Caribbean world (in which *I* include Guyana). At least, more than there is to support an idea that it originated elsewhere.