If you're running in "leaf" mode, & the majority of people do, then incoming searches do in some way relate to your shared files; ie: one of your shared files has shown up in their search results. You can check which files get hits by going to the Library window, clicking on your shared folder(s), looking at the columns to the far right. Look at the Hits column. These are files that have shown up in other people's searches. Those in the upload column are ones that have been uploaded either partially or fully or attempted.

There are no usernames for LW users. Not unless another gnutella client program allows this, but AFAIK all you're seeing is the search terms in the monitor window's incoming window.