I just got off A4O-SE and the on-board cabin indeed matches what Oman has on their website and post #41 here. Row 15 it in it's on tiny cabin. The lavatory in front of it is a single lav that opens to the K side resulting in 15A being a very quiet seat without noise/light pollution. Before departure I snapped a few screenshots of the WY and JL website that both showed the cabin as having two cabins of three and two rows respectively. That's wrong. It's four and one.

I noticed registrations being listed on the storage containers in the galley and chatted with the crew. All two class 789s have this 4-1 row configuration. The only exception are the two Business Studio planes (-SF and -SG). I can provide more photos/proof if that helps.