He says in the interview that singing songs with lyrics sometimes interferes with interpretation. So, Bobby McFerrin tries to teach without words. He says that not many people can do it - babble nonsense syllables - for minutes on end.
Speaking of language that McFerrin uses:
Is singing for entertainment. Is it for more than entertainment? Inter-tainment?
He is full of endless word-play continues. In fact it calls it 'catching song' not 'singing song'. Words sometimes obscure meaning, but sometimes they can illuminate, especially when you are as original as Mr. Bobby McFerrin.
Bobby Ferrin: Catching Song.
Link to .mp3 of interview