It has happened to one of my sites before, however, it was a brand new keyword (i.e. a long tail keyword related new product launch) and so it doesn't really mean anything. Google is fairly incredible at how quickly it indexes content these days (particularly if it is news worthy / viral) and so I read nothing into it.
A month on the site is still there, but it will be a year+ before people start searching for the term and so it should have finished bouncing about and be fairly well established in its position by then.
(Associated hint: when a big product launch is announced, don't necessarily chase the initial traffic, think about what people will be searching for 6mnths+ / a year / 3 years down the line and build in anticipation of this).
