when you search some term in google, google return page contain that keyword. But fact is that page or open google cache of that page both updated and has no such keyword at that page. What i guess is google use old data for search, new page , though that is indexed, is not used for search.
I am not 100% following what you are saying... But there are many factors for search engine ranking, if 10,000 suddenly linked to my website with a link text that wasnt even closely related to my site; the odds are that I would still most likely rank high for those keywords... There have been some scams out there in the past where people have started a rumor (news) and tuns of people link to their story with certain keywords; only to find out the store was false... Backlinks and link text have a lot to do with the rankings.
Check out the Wikipedia article on Google bombing: http://en.wikipedia.org/wiki/Google_bomb You might be seeing a similar effect on a smaller scale.