OK, maybe I should have said "caused" by detonation.........
I still believe it's detonation the OP/tuner heard,, and was the cause of the damage shown to that head.
I can assure you the ring lands are collapsed to some degree on at least one of those pistons.
Edit:
After looking at the pics enlarged, it appears to be pieces of valve guides, and ring lands / rings scattered around the chambers.
Post those pics up on the Australia RB sites and see what they have to offer. I'm sure that is a image that has been seen often.