It might just be a lousy IT system sending you a cancellation message at the point of offloading. It is strange though that the agent did not clarify it (perhaps the agent preferred to avoid discussion).
Whether for cancellation or overbooking, the compensation should be the same. Airlines would not offer more for voluntary stepping off, than for involuntary one.
Last edited by SK2751; Apr 19, 2017 at 12:45 pm