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Sometimes, when searching your your kw/kp in an inventory like WT or OV, the results can be tainted by a popular website linking out to a search on a specific term or phrase they want users to see. For example, if I was an editor on about.com and I wanted users to read about a specific car defect that occured on early model lamborghini's, I might tell users to CLICK HERE FOR MORE INFORMATION. Then point that link to a search results page for "The_problem_with_older_lamborghini_models_with green_paint". Next thing you know, the SE has a large number of search requests by unique users for that phrase.
Now, if you understand that, there are also some pretty neat things you can do with it. ;)
Another factor that can cause random kw/kp to display is snowballing. In the kw/kp minning world, sometimes researchers (seo's/sem's/B_pushers too!) locate a random phrase on a Top 100/500/10000 (or similar) reports. Then, thinking that they could gain some traffic from this term/phrase, they do a search to view the results. As more search for it the perceived popularity rises, thus causing even more searches.
Also, it is good to remember that these systems can make simple mistakes causing unexpected output.