So to sum up the article, most meteorites (the ones that actually hit earth) are the result of just a few (perhaps three) large asteroid collisions some time in the past.

Most asteroids seem to be in relatively stable orbits which is basically necessary for them to still be orbiting. So it follows that it would take something altering that orbit for them to end up in an earth intercept course. Ejecta from a collision makes sense.

I guess the truly surprising part is that most of the samples we have are such good matches that we can conclude they belonged to the same individual asteroids.