I think his source is the JWfanpage but from what I understood the chants in the duel trailer were collected from the original soundtrack and then mixed with trailer music.
I doubt there is a soul on that site who’d think that trailer track was Williams. I don’t know where that info is coming from but there’s no way it’s true.
I tried watching that video and I just can’t. So much of what he’s saying is way off the mark.