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.
No one on there said that. They’re smart enough to know what is from Williams and what isn’t, and that trailer music is clearly too “epic” to be from Williams. I don’t think the guy in that video knows what he’s talking about, he’s just whining about something he clearly has little experience in.
EDIT: And the rest of the video doesn’t make any sense either. He praises music that is clearly tracked as being from Williams, and the condemns music that is clearly from Williams as being tracked. His definition of themes is completely arbitrary, and only exists so he can make this great score seem like the worst thing ever.
For example, he condemns the movie for putting the Star Wars theme in places where it doesn’t refer to Luke, and for putting the Imperial March in places where it doesn’t refer to Anakin, as if those themes are supposed to be for Luke and Anakin instead of Star Wars and the Empire. There’s a reason they’re not called “Luke’s Theme” or “Anakin’s March”.
Well I wouldn’t go that far (the main Star Wars theme was written to represent Luke specifically) but yeah, it’s far from unprecedented for Williams to use themes incidentally (to fit the emotion of the scene, rather than the specific subject matter). Luke’s theme and the rebel fanfare are each used a few times throughout the prequels to represent heroics in general, and Duel of the Fates didn’t have much of a connection in the Phantom Menace beyond “conflict.” Plus, a few of the themes written for TLJ were specifically tied to emotions, rather than characters.