My guess definitely is an increase in floor height, resulting in the fewer units and floor area with a greater height. I'm less convinced that the floor plates will be smaller.
I've already been spectacularly wrong on this thread (and others), but that's not how density calculations work. An increase in the floor to ceiling height doesn't mean a reduction in units or a reduction in the floor area. Floor to ceiling height isn't part of the density calculation. A decrease in the overall gross floor area, while still keeping both towers, means the floor plates have to have been reduced.
Are they going with taller floor-floor heights, maybe for the luxury market?