He had two bombs in the 1st Q - think the knuckler was because the ball moved a bit on him on the tee. Wind is blowing from right to left from the perspective of the TV.
I've always wondered that myself. The only thing that I could come up with is Julian is more shifty and quick than actually fast (as in straight-line speed). You need more straight-line speed for KR's (Blount being the exception I guess). You need more shiftiness on PR's. Maybe that's why.