A muqaddimat al-kitab concerns the arrangement of a particular written work, rather than only the necessary prerequisites of a science:
قُدِّمَتْ أَمَامَ الْمَقْصُودِ
It has been placed before the principal subject.
An author may place a statement of purpose, chapter plan, key terminology, or benefits of study before the main material. This is introductory discourse in that book, even if another textbook might teach the same science without precisely that introduction.
It is identified by its position and usefulness in relation to the book's principal purpose.