Presume Mensabum’s statements are correct and there is little unconscious adjustment to correct any inaccuracy of his aiming method.
How can it be that
Mensabum learned this method from a pro who had learned it from another pro;
It appears to work for many players even though Mensabum's method is inaccurate?
Part of the answer may be in Fastone371's observation that it's impossible for Mensabum’s cue-ball contact point to contact the object-ball contact point.
I dont think its even possible to make the contact points touch in the top photo
In using the method, one looks from the cue ball toward the object ball, and lines up the two contact points —regardless whether the contact points can actually contact each other.
In parallel-line method, the two contact points line up so that the cue ball hits OB at contact point. Not so with the Mensabum method, however.
If one draws lines between the contact points of the two aiming methods, the two lines intersect. Although the Mensabum method has a contact point more distant from the cue-ball edge, the line for it crosses the parallel-line method and lessens the inaccuracy between the aiming methods.
That and the imprecision in aiming using either method makes Mensabum's method as successful as the parallel-line aiming method for many shots.