Has to do with location of equipment and position of axles. The 25FB would be a better towing trailer than the 23FB without any load.
But the 23FB has most of its storage space up front. When loaded it would see a substantial increase in tongue weight, a greater increase than the 25FB I would guess. The location of storage tanks also come into play here.
We can hope the engineers have considered all factors to ensure both trailers will tow well when in use. Note that on most models heavy kitchen equipment such as range and fridge are near the axles to aid stability.
I wouldn't select a trailer based on unloaded tongue weight unless you don't plan to take anything along. Using a tongue weight scale, you have some control of this weight, but keep the heavy stuff near the axles and have at least 10-12% total trailer weight on the tongue.