Supplemental results ranking well

Supplemental page appears high in SERPs

[diamondgrl]

For the search for my site "Blue Widget World", Google returns >100,000 results. My home page appears first. The second listing from the bluewidgetworld dot com site is a page that has the "noindex" tag and appears as a Supplemental result.

Since the site has thousands of pages in the Google index, why would a page from the Supplemental index be ranking as the second-most relevant page. Incidentally, this is for a site that lost most of its Google referals March 23 so I'm continually looking for clues about what might have caused it.