If it was very sudden, very short in duration and quite abrupt then it could have been the wake from an another aircraft. It happens occasionally depending on a range of factors.
All I can think of is how would anyone know it was just one wing? You can't get a good view of both wings from within the cabin at the same time.
It was probably a non event. Passengers have a habit of over dramatising and can make a normal flight out to be a close shave with death when in reality there was never anything wrong.