I have heard differing viewpoints on this topic of crushed existing building materials as fill onsite qualifying for this credit...? One of the practice exams I took included fill from crushed concrete slab as “reused material” as a correct answer. I understood that this case qualifies as “remanufactured material” and can be applied to this credit, but wording on this website does not agree.

The comments are from this site under the credit “Bird’s Eye View”:
We are demolishing an existing building, crushing the concrete and stone, and using it as fill onsite. Does this count under MRc3?

No, as the material is being "re-manufactured' into something else, it is different than reuse, where products and materials are used intact, but in different applications or locations. The primary environmental attributes for this case are construction waste management (MRc2), and potentially recycled content (MRc4), and regionality (MRc5). The intent of this credit is to extend the life of existing building materials.