From the PostgreSQL DDL script for the "assignments" table, the columns EXCLUDE_BIBLIO and EXCLUDE_QUOTED have the same comment.
Here's the comment:
Selecting this option will exclude text appearing in the bibliography, works cited, or references sections of student papers from being checked for matches when generating Similarity Reports.
While the two columns are similar in function, the comment for EXCLUDE_BIBLIO doesn't directly apply to EXCLUDE_QUOTED.