Jesus wept, why are so many people trying to play amateur detective?
The ground it is on appears to be flat concrete, perhaps half derelict for a while, with pieces of broken concrete and some plant matter (such as might grow up through joints in old concrete) nearby.
But I'd distrust even that cursory look at one picture and it may turn out to be quite flat compacted soil.
Any impact can produce witness marks on both items, such as scratches in the rotor which may match scrapes on the other object, with paint fragments left on one or both objects.
I say again, leave it to the professional investigators, with access to far better evidence than a telephoto lens picture, video from a different day, fourth rate guesses based on third hand rumour of what some unidentified person may have said, miscellaneous other stuff.
since you quoted me, I'll offer up my personal experience that I have been involved in many component inspections that have been in accidents. I'm not some bloke guessing here. I've seen plenty of damaged parts in my career. I have been involved in some accident investigations because of my experience, those investigators ask questions because they dont have the answer. My experience and other like me, have helped them find their answers. So while you might lump me into the category of amateur detective, I have a bit more experience than that.
I know the limitations of what a picture can offer, but I see in that picture evidence that offers alot of information to the possible cause, and alot for post incident.