In an old film, I recall the witness being sworn, "Do you swear to tell the truth, the whole truth and nothing but the truth?" The witness answers with a quote from the classics, the essence of which is the question you pose, "What Is Truth?" The judge bangs his gavel and sentences the man to 30 days in jail.
No idea now what the film was about.

With very simple songs, it is easy to say that they are descended from something older, when 'in truth' there is no relationship. Or vice versa.