I heard that having that kind of wing movement would give them a higher top speed on the straights and also introduce more favorable balance (on the under-steer side) going into high speed corners.
I can pretty much confirm that this is not some kind of hoax from the Spanish media. I've seen a lot of credible sources (Adam Cooper, Scarbs, Rival Engineers, etc) talking about it and the reply from Charlie Whiting is completely legitimate. It is either one of 3 things, a weird manufacturing fault, a clever performance enhancement, or an attempt to get the rules made more strict in order to hurt Red Bull. I'm pretty sure it'd be the 2nd and I think it is unfair if McLaren get told they have to change it even if their front-wing passes the required tests, because Red Bull were clearly doing things they shouldn't to observers via video and pictures yet so long as they passed the tests, it was deemed legit.