Archived bundles of files having significant names are important! Torrents of opaque disk images and archives (e.g. pirated software) or video files (e.g. pirated movies and TV series episodes) might be popular, but the strong suit of BitTorrent are carefully crafted and often very large collections of books, music, emulator ROM files etc.
Reading the page, it sounds like they're talking about the "torrentfs" mounted filesystem component, where read requests will download just that part of the file.
So theoretically, you could open the archive in a GUI, extract the file you want, and the only part it would download would be the archive header/file listing and the part of the archive corresponding to the file you wanted.
Of course, this wouldn't work for tarballs or solid RARs, but for regular archives it could conceivably work.
Search result priority is largely irrelevant for rare or specific files, since there are going to be few results (at least, few clearly different torrents) and each result is going to be inspected by looking at the file list.
Indexing file names is the search quality improvement you need most. For example, I tried searching for "Pretty Polly", by the Poison Girls; moderately popular niche music.
There are 0 results for "pretty polly" and 2 results for "poison girls", one of which is a complete discography collection containing that song. Imagine the results for more popular and prolific authors.
