Hello!
I doubt the pitted piston crown was subjected to just "detonation" (wrong ignition point).
I have experienced these pitted pistons many times before in F3D pylonracing when we ran Rossi and MVVS 6,5cc engines and the pitted pistoncrowns was allways caused by running our engines too lean so that the glowplug filament melted and burnt small holes in the top of the piston crown and sometimes scoring the sides of the piston.
So if you experience such a piston ...be very carefull and look for any scoring marks on the piston and on the cylinderliner.
Look also for a combustioncamber that is totally sandblasted from small glowfilament remains!! And look out for glowfilament remains inside the ballbearings.......

Regards!
Jan K
Sweden