I don't know why I get such a kick out of a story like that. I guess it is the way that it demonstrates (giving everyone the benefit of the doubt) the folk process at work. It is like seeing evolution taking place before your eyes. It's possible that Behan thought it was an original tune and his complaints against Bob Dylan were sincere even if wrongly based.
I think what the story does show is that all those people were smart enough to recognize a a good, evocative melody when they heard it.