A site is a site is a site whether or not it's a forum. The referrers section lists other blogs and web sites that link to your blog. A view is counted as a referrer when a visitor of the other site clicks a link and lands on a URL of your blog.
Why doesn’t the number of referrers add up to the number of total views?
Not all visitors will land on your blog by clicking a link somewhere else. Visitors may type your URL directly into the web browser, click a link in an email, or click a link in another application which then loads the browser. Visitors that come from search engines will also not be counted as referrers because they’ll be listed in the search engine terms. http://en.support.wordpress.com/stats/#referrers