Forum Moderators: open
Secondly, I wonder if those pages link to a URL that redirects (or did redirect to) your page; or that has (or had) identical content? Either of those things could credit you with the links.
Looking at it more seriously (as difficult as it is for me to be serious ;)), if I were presented with this situation I'd try to evaluate the link text opportunities and focus on one good one to build on. I.e., if I thought I could make money in a horse theme, and if I had some links that read, "horse trading", I might choose to target the site with that as a starting point.
Since this site is currently showing PR5, though, that isn't such a stunningly good PR to justify a major project IMO. A few decent links can get just about any site to PR5. The best idea is probably to keep the site going in its current use and see if the apparent PR boost helps it meet its original objective. This linkage/PR situation could be a transient artifact of the current update process, too, so I'd probably let things settle a bit before I put a bunch of new work into the site.