The FIA has placed ever stricter limits on wing flex and has in place this season even tougher tests. But crucially these tests are static. The theory goes that it's not the Red Bull wings that flex but the whole nose, to which the wings are attached, flexes at speed and alters the angle of attack of the wing assembly.
This is not specifically illegal under the current regulations and deformable component aero is a concept car companies obviously are well aware of, consider the deformable front spoiler element on the Ferrari 458 Italia, it certainly does not seem pass the "movable aerodynamic device" smell test.
How is it done is perhaps the bigger mystery. How is the flex controlled? Structural engineers out there will be able to advance theories of carbon sheet and polymer construction allowing it to flex the debate is open on the genius vs evil genius bit. For sure Adrian Newey is a champ at racing those gray areas.