Hmm. I'll have to think about it but I don't quite see yet how this ensures that for example all documents containing all four words of a four-word query will b

Hmm. I'll have to think about it but I don't quite see yet how this ensures that for example all documents containing all four words of a four-word query will be ranked ahead of documents containing three or fewer words of the query. Mere angle between two vectors would for example mean that a "document" consisting of three words of the query could be ranked higher than a document with thousands of words containing all four words of a query, even if the document vectors had tf-idf weighs as components. That clearly is a viable notion of similarity, but that's also clearly not what the type of search alluded to in the article is attempting to do. Plus, your description definitely isn't something I would have been able to divine from the description from the article. Thanks for rephrasing it in comprehensible English.