It looks like there might be some fine metal chips in the crankcase, but other than that I didn't see any objects In there or in exhaust.
Is it common for objects to get inside the cylinder and damage it? Nothing can get in there except through the fuel/carb or something falling down in it while changing the plug right?
It's not common, but bearings do give up the ghost. There are balls and roller parts that cause havoc when they do(give out). If the wrist pin c-clips are clearly still in place I would pull the seals and give the bearings a good going over.