There's a lot of narrative in the article but no source of where his risk figures come from.

Another source estimates the risk to be two orders of magnitude higher (http://blogs.discovermagazine.com/badastronomy/2008/10/13/death-by-meteorite/#.VWBSy_ntlBc):

Astronomer Alan Harris has made that calculation. Allowing for the number of Earth-crossing asteroids — the kind that can hit us because their orbits around the Sun intersect ours — as well as how much damage they can do (which depends on their size), he calculated that any person’s lifetime odds of being killed by an asteroid impact are about 1 in 700,000.