This is an interesting story, contradicting what has been the accepted version for many years.
PS - disco scene????
Could they be referring to the singer in the Fillet of Soul?
Yes, I think so but it's hardly a disco which makes me wonder if the writer actually watched the movie.
Nice link - but doesn't quite make Macca out to be a liar. We are, after all, talking about the notoriously fiery and undiplomatic Harry Saltzman who could start a fight in an empty room. They many not have realised that you take his stuff with a pinch of salt. It may be true the producer(s) thought the finished product was a demo as it has a slightly unfinished feel to it compared to Barry's number; it's partly a rock track after all.
The version of the story supported by the archives makes sense but I guess there may also have been some showing out by Saltzman.