Any question answered...

Isn't this fundamentally the same idea as the Shimano AX stuff from years ago - align the footbed with the axle better?

Does anyone understand this claim?

No.

It's a claim without context, and therefore meaningless.

In general, it is a claim widely made but not well supported that reducing the distance between the sole of the foot and the pedal axis, in some cases to a slightly negative number, improves biomechanical efficiency, which might increase power or reduce fatigue.

It's likely to be the case that minimising this stack height is a good thing, but that nearly all the gains have already been achieved by the time you get to the <25mm of all the common clipless road systems, and if you try to get the stack any lower with conventional crank threads you throw more away by increasing Q (@xavierdisley showed that for most people, standard Q is already much wider than the optimum) than you gain by reducing stack. Nonetheless, many have decided that this is the hill they will die on, from the 1898 Ramsey Swing Pedal via Shimano Dynadrive in the 1980s to Steve Lubanski's Side Mount Pedal in the first decade of the present century, and all have disappeared without trace.