You realize that they have data on pretty much everything that happens in game, they just have to put something in place to use it. So, if they are getting reports of a player leaving warzones just before the game ends (who would leave at this time, you get no rewards after playing an entire match), then they can look at the data to see if that is the case and take appropriate measures.
AFAIK they've never needed videotape to ban hackers, I don't see why this would be any different if players are found to be continuously leaving warzones to avoid XP.
I know they have data on everything that happens in this game. But data cannot account for INTENTION. And since leaving a WZ is NOT a bug, BW doesn't care that people are leaving WZs to avoid xp. I say they don't care, because this has been going on since the game came out, and there has not been ANY mention of this being an exploit by BW, nor has anyone ever been banned for doing it.