Mujmal admits multiple relevant possibilities and requires explanation from the speaker to determine which is intended. In the book's example, the technical boundaries of riba can be understood through pertinent revealed explanations.
Mutashabih represents greater concealment. According to the book, its specific intended reality cannot be established through ordinary linguistic or juristic reflection, so restraint and acceptance of the true intended meaning are required.
The categories differ in their practical posture: mujmal calls for authoritative clarification leading to determination, while mutashabih calls for caution about claiming to determine what is not disclosed.