The clutch has steel and fibre plates in it.  The shavings could be from the steels. Have you pulled the clutch yet?  Also look for wear on the drive gears on the clutch side.  And yes, poor maintenance, clutch slipping could cause this.  Could also just be normal wear from age.  Previous owner probably never adjusted or replaced the clutch.  Who knows?  You find all kind of things buggered up on these old bikes.