Good question?...
That's a good question but there are way to many varibles that can cause this type damage.  Detonation is a probably cause.
You'd have to investigat the oiling, the fuel, reading the spark plug and so many things.  I don't think anyone can give you a definitive answer on that.  Now, if you got a hole in the top of the piston, that would be easy.  Your oil pump quit, you ran lean and burned a hole.
What I'm trying to say, is it's hard to determine that type damage.  But before repair, you'd need to find the "root cause" to this.   :cheers: