It does indeed have "Operated by Thomas Cook Airlines" when I try to book it on their site. However, the layout in Premium Eco is 2-3-2 up to row 9, then row 10 is also premium eco, but just the middle 3 section (it shows no outboard seats for row 10. Then regular economy starts at row 12 (no row 11).

That doesn't seem to match the A330 layout on Thomas Cook, where Prem Eco ends at Row 8.

So... I wonder what this mystery plane is?

They haven't started the route yet this season, otherwise I'd check on Flightaware and get the tail number.