Asteroid Dimorphous easier to move because it's made up of rubble?

[DaveC426913]

TL;DR Summary

Do rock pile asteroids behave differently than classic inelastic collisions?

"There’s really no cohesion between different pieces of gravel or rocks on Dimorphos. That makeup explains why DART’s impact made such a such a surprising change in Dimorphos’ orbital period, decreasing it by about 34 minutes. A collection of boulders is easier to shift than a solid object."
https://www.universetoday.com/168008/the-surface-of-dimorphos-is-surprisingly-new/

I would have thought an elastic collision with a solid object would cause more movement than an inelastic collision with a rock pile.

Is there more nuance to this?