I had a look on ExpertFlyer for late December. The 789 is scheduled. I do note that the biz availability & cabin seat map look very full except for a few seats.

So either an aircraft change is pending, OR (something such as) they have started an agreement to sell portion of their cabin under a codeshare. Qantas does this on Asiana, which had me well confused until I discovered the nature of the agreement, whereby not only is there a codeshare but also a fixed allocation of seats for Qantas' own customers - rather like a dedicated mini-cabin.

But who really knows....