Hi Stephen Sounds like a lean mixture may have caused the high revving. Lean mixture may be caused by shotage of fuel thru several causes such as stopped up vent in petrol tank, partly bocked main jet in carby. Carby manifold leaking air thru coming loose. etc etc . Whether the high revving caused the scoring its hard to say. The oil content may not have been high enough to cope with the higher speed ,it would depend I would think on just how high it did rev and for how long.
Without seeing the piston itself it is hard to guess the cause..... If it is just one deep type of score then it may be possible thru some foreign body passing thru the engine, A chip off a engine bearing. or screw form the choke valve ot the throttle valve . I have seen this type of damage afew times . Bits of big end needle bearing were a common cause on various makes of chainsaws causing bad scores on the piston..
I dont know the design type for the engine you have so cant say much more Cheers Joe
