That was heuristics. It looked for the text "more" or "next" or "->" within an anchor tag. Sometimes it would be fooled if a forum thread or other link had a title containing one of those words.

Heurisrics augmenting a (half-)standard[1,2,3] that, in a more idealistic time, some people cared enough to follow: <link rel="prev"> et al.

[1] https://developer.mozilla.org/en-US/docs/Web/HTML/Reference/...

[2] https://microformats.org/wiki/existing-rel-values#HTML5_link...

[3] https://www.iana.org/assignments/link-relations/link-relatio...