The results showing are those articles in the PubMed Central Collection in which the "Reference Author" was cited.
The PubMed database offers a limited version of cited reference searching. PubMed records which are cited by articles in the PubMed Central database, can be found on the abstract page for a record. You can look for them on the right-hand side of the page, below the “Related citations in PubMed” section. The cited references link to the PubMed records, which in turn link to the full text articles since PubMed Central is an open access database.
Cited reference searching starts with a specific article, book, or other publication. Usually your first step is to find that publication in the database you are using. That may mean searching the title, but sometimes you'll use the author's name. Since citations for this publication can vary, expect the need to select from among variations or to perform multiple searches and combining the results.