Most information online suggests that domino effects are not classed as exceptional circumstances. Exceptional circumstances are meant to affect the flight in question directly. There looks to be a case that is regularly quoted - Jager vs easyjet that supports this. Relying heavily on a single plane to go back and forth with no backup is a risk CX chooses to take, not one that the passenger chooses.

On this particular flight CX had ample opportunity to make alternative arrangements as they knew it would be delayed many hours before the scheduled departure time. They had an earlier flight that evening which they rebooked many passengers onto, but did not contact me to offer this or in fact make me aware of the delay. They could have also rebooked us onto the VS or BA flights departing to HKG that evening.