I imagine it has may have become rather fashionable to allude to multiple successive asteroid impacts after the Shoemacher-Levy Jupiter impact pattern...(?)
Shoemacher-Levy was a comet, the mechanism for a comet breaking up in space is much better known than that of an asteroid. There are many examples of comets fragmenting.
Multiple impacts may tend to point to a comet as being the agent of the death of the Dinosaurs.