This thing came in at significantly greater than orbital velocity, faster than it can fall from any earth-bound orbit, and in the reverse direction from pretty much everything launched from Earth's surface (in all the wide-view videos you can see it approaching from the direction of the rising sun, in the East, and comparison of the shape of the trail with http://www.youtube.com/watch?feature=player_embedded&v=VdoKEFsemvw confirms this). It also looks JUST like any number of other meteors that have hit, and discharged as much energy as a 300 kiloton* nuclear weapon as it disintegrated (in a long streak, not all at once) - far more kinetic energy than anything human launched has ever carried (a fully fueled saturn 5 exploding with all of its original chemical energy would release less than five kilotons). Energy couldn't be generated in space either, a 100 square meter solar array would require 1400 years to gather that much. And if you were going to deorbit something you would rather blow it to pieces over the ocean where nobody's ever going to find all the tiny fragments scattered over hundreds of square miles of seafloor.

Conclusion: Natural. Not bothering with probability estimate.

Not only did it come in on a completely different trajectory from the known asteroid (closer to coplanar with the ecliptic seeing as it came from the East), but Russia was not even visible to objects on similar trajectories to the known asteroid until after it had passed the Earth. The chaotic influences of the rest of the solar system and inhomogeneity of impacts also mean that even if you expode something into lots of fragments on completely different orbits (which does not really happen) they are NOT going to come to the same spot within 50,000 kilometers at the same time on their way back together. The 'focusing' effect of the Earth's gravity exists but is insufficient to wrap around the zone that something cominig from one side of the earth can hit to more than a few degrees away from half of the planet at velocities this high.

There are plenty of these rocks throughout the solar system, and they DO hit the Earth. Something this size ish happens every few (single-digit) years, its just that most of the time they happen over the ocean, desert, or sparsely populated land. This one had the 'good' fortune to explode directly over a city of one million people well-armed with anti-police and anti-insurance-fraud dashcams.

Conclusion: Unrelated to known asteroid. Not worth probability estimate.

NOTE: There seems to be some question about the total yield, but given that the shock wave took a minute or more to reach the ground from tens of kilometers high from what I have read, and still had enough force to shatter windows and blow in doors, I'm leaning to the higher end of the estimates. EDITED: the USGS says 300 kilotons according to their analysis of seismographs.

EDIT: Just realized something interesting. It came from the direction of the rising sun - meaning that, even allowing for gravity bending its trajectory a bit, it would have come from a trajectory at most probably a few tens of degrees away from the sun in the sky. I do not know much about the estimated size of this thing, but that would indeed make it much harder to see as that part of the sky is only visible at night for a very short time and through a large amount of atmosphere. Even though we are getting better at detecting incoming rocks a few days out (a few years ago we even caught something only like 5 meters wide a day in advance and predicted its impact site, though that was a special case and we don't catch even a fraction of what actually comes our way) this one would have been particularly hard to see.