It appears (from reviewing the source) that this plug-in only auto-internet-archives the Known posts themselves, and links only in bookmark posts.

Expected behavior:

• auto-internet-archive ALL links in ALL posts (e.g. all links in notes, all links/citations/references in article, all in-reply-to links etc.)
  I.e. all pages that Known (even attempts to e.g. does discovery on to) send Webmentions to, this plug-in should send to the internet archive for archival.