Chainsaw Repair

Got an 084 in that was locked up. Pulled the front muffler cover found piston pieces and ring pieces. Only on the exhaust side. Trying to figure out what happen no seize marks. Bottom end bearings are good. A little play in the big end bearing but have seen worse.  The cylinder looks good and salvageable. No deep score marks. Could it be from over speed? Or just a faulty piston. Guy said it was rebuild not that long ago. And yes the piston was installed correctly.