MSN.com will often include direct links to Bing searches relevant to articles or news items. If you rank well for the linked term, then you'll see a traffic spike. For me, the pattern has been a massive traffic spike for a single keyword which trails off for the next twelve hours or so.
This doesn't sound like what you experienced, but perhaps it's a helpful clue.
This doesn't sound like what you experienced, but perhaps it's a helpful clue.