No, it's mastering. DTS HD is stored as discrete channels and thus each channel is played separately and independently. The only time any mixing occurs is when it needs to downmix because you lack sufficient speakers -e.g., playing back a 7.1 soundtrack on a 5.1 system means the surrounds are mixed together.
But the mastering engineer is free to put the audio where they want. If they want dialog to come from the front they can, and mix in a little of that dialog track into other channels to make it more realistic. But if they want,they can make it come from just the center channel. Some directors, like Nolan, don't do surround sound so they pretty much put dialog all in the center channel. However, the mastering engineer might put in effects on the left or right to correspond with screen action (and Nolan's style may mean very little goes to the surrounds - he wants it to be all from the screen). The score composer may put the music all around so it surrounds you since it's background.
There are good mixes and there are bad mixes. The Blu Ray you used might be a good one. It can also happen the other way. For a while there was a three way argument on these forums about Dolby TrueHD, DTS HD and PCM sound tracks and which sounded better. They're all multichannel lossless coding, but the arguments went on and on, mostly because it was difficult to find a disc with multiple encodings on it. It's easier these days since you can find Blu rays with DTS HD, and the UHD Blu Ray with Dolby Atmos which can run in compatible Dolby TrueHD mode. And there were arguments over Dolby digital and DTS lossy encodings, again, there were only a few DVDs that were available that had both. And even then you ran the risk that the disc was mastered twice rather than merely encoded.
In your case, it should be much easier since the xbox should be able to play the file too off a USB drive.
