I think he was referring to hearing the DotF chants as diagetic singing coming from the Sith cultists during the climax.

It is sort of ironic. John Williams and Abrams seem like they were going to make a new track for Luke raising the X-Wing, but many people around them said it just had to be the same music from ESB because the fans would know it. The Duel of the Fates track seemed like a no-brainer. It even showed up in the marketing, and the duel seems like a great place for it. Is it because it is the from prequels? Hmm.