Just because he looks like hes doing a flat 3 but only does a 180, doesn't mean its a "flat" 180. There is no flip. He is on a flat axis the whole time, he just does a 180. But, due to the camera angle and the fact he's on a different jumping plane (quarter pipe) its clearly just a 180.
Think of it this way, if he was hitting a normal qp, could he have landed the 180? if you look at  the shot in mid air, he does lean into the other tanny, but he could have leaned forward to to compensate for a normal qp landing. granted, they aren't perfect QPs but still, imagine if in mid air he went into the normal qp tranny. All he does is pop like its a normal jump and does a 180 over the camera and you get the illusion that he is doing a flat spin, but in reality he's doing a normal 180.
Im very interested to see this from another angle, because yes it could possibly be a on a slight axis but from the angle in the trailer, with the camera position and movement, its very deceiving.