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My best guess is that you saw a 'fresh' listing. These listings are supplemental to the normal (monthly updated) database. Sometimes, they appear for a day or two and then vanish. If the site continues to link to the article then it may reappear at the next Google Update [webmasterworld.com].
Changes in Google due to fresh listings are explained well in Marcia's Everflux thread [webmasterworld.com].