As I mentioned, the "I'm sorry to say" verse is traditional, and turns up in field recordings all over the Caribbean. I'm reasonably certain it did not originate with Burgess, though I'd have to look up the dates on various field recordings to be sure. So that verse at least is something Belafonte could have heard as a child. But, as several people have said, it was more about marketing than the truth. Remember also that Belafonte was an actor, too. He may have approached his concerts as role-playing in that sense, and lied effusively under the cover of "staying in character."

Calypso is an interesting genre, one of the indigenous folk/popular styles out there in which songwriters are given credit for their work (but still liberally steal from one another). Burgie just took it to a new level by going to Juilliard, performing and writing for broadway, etc. But the genre itself is difficult to pin down on the folk/popular continuum.