[See my post following the one you quoted.........it speaks to "lazy eye" the lay term..........i.e., amblyopia the medical term.
Too many causes of amblyopia to specifically comment on your brother's experience, but covering Watson's good eye would not miraculously cause his eyelid to elevate off of covering part of his pupil. The pirate technique is most likely to be helped when dealing with a "wandering eye"......a strabissimus muscular problem, in hopes that the muscles can be retrained. Typically, if amblyopia has already not occurred, it can be corrected by correcting the source of not using the deficient eye. However, if the source is severe ptosis and is present at birth and addressed only after childhood, it seldom is reversible by surgery. When you see ptosis in particular occur first later in life or only very as is obvious with Watson (see high school picture compared to the most recent), the ptosis condition commonly becomes worse, the pupil becomes more covered, and eventually the patient will "turn off" the other eye to the brain because it is getting in the way of clear vision. However, in adulthood, simply surgically lifting the affected eyelid will uncover the pupil and allow the patient and his brain to readjust tote full peripheral field of vision once again..........since irreversible amblyopia has not occurred
If you want to prove this phenomenon, just tape one of your upper eyelids down from the side so that your upper lid covers half of your pupil. Then, read for a while and you will quickly notice that the annoyance causes you to start reading only using your untaped eye.