Okay .. all this is a little vague...

You booked on CX but AA issued your ticket? Was it AA codeshared? Why was the reservation cancelled? Who cancelled your reservation? If it's a CX flight number and no ticket number is on the PNR within about a week prior departure, CX will automatically cancel the reservation. If AA booked this, they should have known about this as CX's CRS would have sent a message to AA.

If your reservation had been cancelled, AA would not have been able to reinstate your reservation so close to flight time. CX's CRS closes out all reservation bookings within 10-12 hours of departure and no new bookings are at all possible. If they're booked on the AA codeshare, well, there might be a booking on AA, but as far as CX is concerned, you don't exist as there isn't enough time to generate a confirmed message to CX. CX ,would have by that time you checked in, already processed upgrades if any, on their flights and well, you lucked out as I'm sure you would have been considered for an op-up especially if you're on a full J ticket.

You could have gone on JL , you know... on an AA codeshared number and earn the extra Plat miles. But glad you got your KE flight in the end. So what did AA do in the end? Endorse your ticket over to KE or you refunded that ticket and bought a new one with KE at the airport?