meaningfully and strongly related and how focused they are in providing a well-defined purpose to the system.

A class is identified as a low cohesive class, when it contains many unrelated functions within it. And that what we need to avoid, because big classes with unrelated functions hamper their maintaining.

The answer : "subtypes of a high cohesive won't need to override most of the methods" , has nothing to do with high cohesion.

The answer: "other classes, which use a high cohesive class,won't need to know the implementation details of this class", has more relation with encapsulation than high cohesion.