When I run a search for "foo", what am I searching for?

Obviously, for entries that have "foo" in their names. But I get lots of results that do not have "foo" in their names, so apparently, there's more information available that can be searched on.

Is there a way to view this information?

A couple of that is just spam. Some clients match search results against available meta information, for example, MP3 ID tags or simpler against the directory name in which files are located. LimeWire sends some meta information attached as XML data which you can see in the GUI. There is a way to search by meta information using XML queries but it's questionable how well this really works. It might work fine for MP3 files as long as the tags are correct but for all other files it probably doesn't work too well because such meta information cannot be extracted from the files. Users would have to provide this information manually.

I thought this was Gtk-Gnutella

Yeah what? LimeWire sends it, everybody receives it. Even Gtk-Gnutella.

So basically it is information that is available on the sharing host only, except for the XML that LimeWire transmits.