I think they measure one of them upwind and one downwind in a further effort to eliminate variables. They also try to use the holes where the players will most likely actually use driver. More on the driving topic dufferole:
http://www.golfwrx.com/forums/topic/...ving-distance/
https://www.golfchannel.com/video/to...longest-drives
https://www.titleist.com/teamtitleis...-to-be-reduced
https://thesandtrap.com/forums/topic...ving-distance/