That is a necessary but not a sufficient condition, as the type of rock involved, called carbonaceous chondrite, is found in other asteroids, too.

ECONOMIST: Asteroid impacts

Assuming that the figure was similar during the Cretaceous, it would be a long shot that the first fossil meteorite to turn up from 65m years ago was made of such a rock unless a huge extra supply of carbonaceous chondrite had suddenly arrived on the planet.

ECONOMIST: Paleoforensic science