Okay, I recognize those markings from my motorcycle; the cylinder head also had almost the same markings, just a slightly larger number of them.
After disassembling the engine, it turned out that one of the piston rings was the problem , and it's worth noting that this cylinder obviously also had a piston eater.
A piece of metal lodged in the cylinder creates hundreds of impact marks on the cylinder head until the engine is stopped. It leaves more than just a single mark; it can also cause immediate engine failure. I had that issue with my BMW Boxer.
'A piece of the turbo? Shouldn't that still have to pass through the LLK (Low-Pressure Coolant)? If it's a small piece, it could damage the turbo, which would be noticeable as an imbalance if it's still spinning. Have you looked inside the turbo to see if anything is missing?' It's not much extra work since the engine is already disassembled.
If a foreign object was in the cylinder, how would that reflect on the workshop's workmanship?
After having paid a lot of money for this in the past, because it can never be proven later, I am now always present myself. (e.g.,) BMW boxer engine with manual transmission and DB 280E engine.