URL pattern matching
Resource pages are predictable: webmasters who curate lists of external links usually give the page a URL that says so, such as /resources, /links, /resource-links, /useful-links, or /links/resources. The tool searches for pages carrying those patterns for your niche, so a result's URL hints at what kind of page it is before you open it. The pattern match is the filter; it does not prove the page links out.