The Technic ball in the centre of the gearbox collides with the axle holes immediately surrounding it. A Technic ball can only be placed like that next to a pin hole, not an axle hole.
The fact that the technique causes so much friction (which is the whole reason it’s used in the first place) is also a clue that it stresses the pieces, since friction comes from collisions between parts, and it is very rare that pieces can collide in a legal way without being specifically designed for it by Lego.
A clearer breakdown of a functionally identical gearbox can be found in the entry for the winning Kualus MOC from the Toa Hagah contest: