«أَمَّا الإِيجَازُ وَالإِطْنَابُ فَلِكَوْنِهِمَا نِسْبِيَّيْنِ»
Concision and expansion are relative categories.
Relative (نسبي) means that neither category is measured by a universal word count. It is compared with a recognized, appropriate manner of expressing that meaning in the relevant setting. This standard may change with genre, audience and purpose.
A brief answer can be eloquent in one context, while a fuller explanation can be more appropriate in another. However, wording so compressed that the intended meaning is lost is defective obscurity, not admirable concision.