I got a feeling this guy's been around for a long-long time, like +100,000,000 years, that's he's fallen into a long term 2/3 resonance with Venus. (Who hasn't?) Superimposed on the long-term resonance is an aperiodic perturbation due to the the effect of the Earth. In fact, a gravitational encounter with Earth may have been what caused him to be captured by Venus. (Like I said, happens to all of us.)
Of course, I'm not 100 million years old, yet, but the older I get, the harder I have to fight my graviational encounter with Earth.
This is little more than a hunch on my part, but what do I know, I'm just a hopeless romantic.
Gotta keep watching though, it fell to zero once before. The "news" page on the NEO site has an article from the 27th stating that the risk had fallen to zero. Then the number rose again to "1".
http://neo.jpl.nasa.gov/risk/2004mn4.html
The one potential impactor that is known won't reach the rendezvous for about 880 years; they don't have that on the main page of close-call objects, keeping it on a page of its own.
http://neo.jpl.nasa.gov/1950da/