No rocket science here, all they has done is add a second intake & move the intake to the back of the air box. It is well known that the XT motor loves more air flow & the cooler air will make a difference.
I did this mod to the XTX/R's a few years ago by drilling 30mm holes in the air box pre-filtered chamber. Once I can get my hands on a XTZ I am sure we will see a few mods from me, I am sure I could come up with something for the air box at half that price.