Height is an easily observable phenotype, cognition is massively more complex and dependent on many genes that are not well understood. Furthermore, cognitive ability is heavily dependent on upbringing, and cognitive ability develops at different rates for different people.
Not to say that the school system should be cookie cutter, but we in no way have enough knowledge about human cognition to determine a child's career path because of their performance in kindergarten.
At that point, probably not.
Assuming a person is healthy, there's nothing that makes playing in the NBA literally impossible.
Well no, but there's a reason that those short people made it to the NBA, they had other potential that got them there. Mugsy was incredibly fast. If it was all about heart we'd see an equal distribution, unless somehow being taller means you have more heart.
Mugsy choose to capitalize on his "small and fast" talent. It's coaches who make the decision to augment teams with speed.
The article says don't practice or work harder... your talent may be enough.