To me there are open questions that, if answered, would help with this mystery...

When was the booking cancelled? Was it still active and ticketed when the pax arrived at BKK or had it been cancelled before then? If the latter, then there isn't much the QR staff could do. My money is on it being cancelled before they even got to the airport.

Who cancelled it? Not sure this is answerable, as all parties seem to be pointing fingers at the others.

Why was it cancelled? Did it fail some automated fraud check? Was the ticket issued by Expedia not properly matched to the reservation?