No, that part of the discussion was about 3 class sold as 3 class, not 3 class sold as 2 class. My own experience is that in this situation the F section is never full, so they don't move everyone they can from the J to F seats, rather it is selective. Diamond status gets the F seats, and who knows what other criteria will get you moved into the F section. The food is still J, of course, but often the service is F level (they even draw the curtains between J/F, despite being all J, and given the Diamond density it is hardly surpirising that the FAs spend more time there.