Oh, you mean the dust shield.
The dealer might have broken it when re-installing it, or it might have been cracked by a road hazard, like a rock, etc.
Pretty hard to prove one way or the other since no doubt the shield is pretty messed up. So I don't think it's so much "facts" as circumstantial evidence here.
The dealer could easily squirm out of this, possibly with justification, but a dealer interested in good will might offer some kind of partial compensation, like a free oil change or some such.
Get whatever you can but don't play attorney because I don't see this unfortunate incident as entirely blame-able on any one person or circumstance.