I hadn't realised how few Thomson (TUI) flights to Dalaman there were this summer. I make it only one per week operated by a Freebird A320. Thomas Cook had three flights each week as did easyJet.
The CAA stats for August, as an example, show a total of 11,829 passengers, with 10,387 shown as scheduled passengers and 1442 charter passengers. I assume the Thomas Cook flights were classed as scheduled along with easyJet, with the Freebird the one shown as charter. The 1442 passengers gives an average load of 180.25 (the CAA includes under 2s). I can't imagine it was any of the Thomas Cook flights as the A321 isn't likely to have had such a low average load in August.