For the pax on CO84, the Mx means CO has to ante up.
For your later flight (are you sure it is CO1152?) you are guessing that the aircraft change was to accommodate pax from the earlier canceled CO84 and the change resulted in the late incoming. Maybe, maybe not. If it was weather, then it was a weather delay for you, but for the original CO84 pax who may have been on the plane with you it was still Mx.