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Tom, it might be the same way that Acrobat Reader ranks first for the query [click here] even though those those words don't appear anywhere on the page or in the source code. In my results, I see only two out of the first 10 results that have anything to do with "click here". The rest are there because of anchor text or other factors. Think of how many web pages you see that talk about "To get Acrobat Reader, Click Here" with the Click Here hyperlinked to the download page. The search engines take that as a clue that the destination is about "Click Here". It's the same way that George Bush's bio page ranked for Miserable Failure, and how many other "Google Bombs" took place (though some are now no longer working). You might take a look at Open Site Explorer and the anchor text on the incoming links to see some off-site factors for the ranking in question.

Thanks Keri for your advice

maybe the best solution is to sort pages with high bounce rate and modify the link structure of those pages