Wikipedia has a good
article about PageRank, the algortithm used by Google to index the pages.
Without going into details, (I don't think anyone outside of Google really understands how it works), Google will assign each website a "note" (called a "Page Rank"). The rank depends on so many factors like valid HTML, traffic size, content, ...
This tool will allow you to check your PR.
my page is clearly more relevant because it contains all the search terms!
I guess Google doesn't consider that simply matching keywords means more relevant. There are other factors to take into account.