As far as I can tell, author is talking about FM-Index. It compresses the search data into a much smaller index memory footprint. I tried using it few times, but never figured out how to use it as a key-value data store.
If anybody is interested, here is the code: http://pizzachili.di.unipi.it/indexes/FM-indexV2/fmindexV2.t...
I guess FM index is just not the right thing to use when you need a key-value data store. It's a full text index -- a data structure, which allows fast substring queries over a fixed text corpus.
