you mean that one site has 2 results directly under each other? someitmes when i do search each site is only lsited once and sometimes there are 2 listigns diretly under each other(second raptured to the right)
I think it is referred to as clustering. When Google finds more than one relevant page from your site for the search term it will display a second or indented result below the first result. Here are some related threads:
On certain search terms it happens for my site, usually if there are many matches on the site.
It think that is what google does. If a site has many matches for the search terms, then the site might get two matches listed, the second indented. There is usually, but not always, a link to "more matches from this site" attached.
I think it is a nice way of indicating that a given site has multiple matches.