I would bet these things are the result of shipwrecks or raft-wrecks where the raft or ship totally disintegrated or evidence of was ignored by the so called “archeologist”
I think it would be safe to assume that there might have been a form of 'ferry' even back then.
So now we have TWO alternatives to add to the 'premise' in the article.
Their use of the phrase "irrefutable evidence" reminds me of the global warming scientists claims of "irrefutable evidence" that the temperatures will climb to 2,000,000 degrees, the seas will rise (or fall, can't remember which), and any humans who don't contribute to funding the scientists careers will die from the heat.
It is possible the first 'raft-builders' were not aware the glue they used was not WATERPROOF.